SDB’s SPORT – An All-Weather Sporter

[prashantjha19]

Thanks to some of you here on this forum, I got myself a SDB Sport recently. This was after a fair bit of deliberation though.

Decently Accurate, Powerhouse of a shooter…..yet light to lug around!

A light one at 3.2kgs.jpg

Well, that’s what I was looking for… and that’s what it is!...., if you do not intend to go through the full text below! A reasonably priced gun, with traditional look and balance, shoots accurate, is really powerful (old habits die hard, you see!) and is so easy to carry around! Too-many-into-one…aren’t they? Honestly, I am only smiling away ….as I write this short review with the Sport by my side. And here’s why…

First shots straight from the factory-A powerhorse.jpg

At 3.2 kgs, it is a great all-day companion for a 50+ years lean frame fella that I am. And with a straight-out-of-box ME in the range of 11-12 fpe with varying pellets is more than what I had ordered for, or can handle with reasonable aplomb. As for accuracy, the photos below could speak for themselves. With my average grade shooting abilities, if I can manage those groups, a good shooter would definitely shrink these to hole-in-holes. In any case, my tuning and research preoccupations these past months hardly leave me enough time to work on and hone my shooting faculties.

Next day sighting in - Accurate shooter.jpg

Loose fit pellets are not for your Sport, at least when its new.jpg

Let’s check the gun out!

I believe it was their Apache model, designed and launched a couple years back, that marked a discernible shift in SDB’s outlook. And what quickly followed was the launch of a series of their new league guns –Gennex, Sport, Artemis, and now of course, the Magnum! Most have come to have good following, too. Curiously though, while they all have better cosmetic appeals and finish, they are mostly the same powerplants as the good old SDB guns of the yore. From the tuners’ perspective, that is THE most appealing facet of the SDB turnaround. That, to me, speaks of their “knack” of air rifles. They seem to have got it pretty good now…..and the best evidence of it is – if you can make an average shooter into a fine one, you sure know ARs! All of their new generation guns in their respective classes are much refined shooters than their past cousins.

Over a week later, more consistent, better power -with its preferred pellet.jpg

So, what would a Model 27 makeover be like!

What would you do if you were to be running an airgun brand…. and one of your models failed to see much sales despite it being nicely made and carrying decent specs (….well, what do you do when you have a market like ours …with mostly crazy-for-power folks around!!). So, what would you do?? Shelving models is the last thing that makers would opt for, because this is a big setback, commercially speaking. However modest, any new model before being commissioned into the regular production line, has usually sucked in a lot in terms of R&D, trials, casting moulds, et al.

The Sport and 27 - Can you spot the difference.jpg

Not surprising therefore, altering and/or tweaking the existing models is usually how it goes; and pretty often ends up delighting the sales counters. Examples are aplenty the world over … look at the turn arounds brought about by the late variants of some successful names -the TX Mk3, the HW77, 95, 97, the Walther LGV, Webley Vulcan, and the list goes on.
So, have the SDB folks joined this league, you would ask!

Well, I would pretty well like to think so! And to the best I can infer, the Sport may be a super-intelligently tweaked (not so much altered, mind you!) refinement of their Model 27! While some may term this more of a wishful inference, I would prefer to revel in this. After Precihole Sports, which indeed is a professionally set up group, if you can spot some of the local, traditional names like the SDBs picking their threads up to match growing demands for more refined air rifles, you would, as an AR enthusiast, like to take this as a welcome thing; won’t you!

I have in the past shared on forums how enormously pleasant a rifle the SDB Model 27 has been. It’s an old model of theirs –something in between the 25’s and the regular adult models like the 45’s. I have nothing that tells me the model sold well. However, having taken an instant liking for it, I have owned one for long, have set it up in varying states of tune, and have only marvelled at the way it behaved in most of these. From young adults to the older folks –all seem to take an instant liking for this low weight, mid-ME, and pleasantly low-recoil shooter. And just before you blink, for the past several months, it has been set up with a Sport’s piston and seal…and (with some of my other mods) has been at its best behaviour, consistency, energy efficiency and output.

I had learned (on this forum, too!) that the Sport weighed 3.2 kgs. Well, my 27 weighs at 3.16 kg, has the same bore, is the same length. No wonder, when I opted for the SDB Sport, I was expecting a gun that was essentially a Mod 27 …but with a longer stroke! I had even opined this on some by-invitation-only forums, too.

Similar powerplants and strokes.jpg

Overall feel and behaviour

I was so squarely wrong though! It came as an in-your-face shock to me! How did these guys manage to go from 7 fpe (my 27 currently shoots at 8.5 though) to in the range of 12fpe that this diminutive looking Sport shoots at!! That’s where I see that the SDB folks may have come of age…in terms of the sheer knack of making fine-shooting air rifles.

I am told most people get cheesed off by technical tuning stuffs, and so I will refrain from going into the specific alterations /tweaking (many times very simple in design and slight in scale) that seem to have worked to make these guns into sweet yet powerful shooters; and would rather restrict myself to just the basics in this post. I believe a smart altering of the compression ratio coupled with a slightly higher rate spring is what did the trick for Sport! The stroke of the Sport works out just one milimeter more than my tuned 27 just nudging the swept volume from the latter’s 38.29 to 38.78cc. Too insignificant a change to account for such huge difference in ME! The spring room, too, is barely 05mm more. So, if you could sense by now, it’s essentially a short-to-mid stroke gun with a pretty high peak pressure. See the photo of the seal post some 200 shots. What does it tell you?

preload at disassembly- A precious lot that.jpg

What does it say of the peak pressure and temp.jpg

Just a wipe and you have a sparkling finish compression chamber.jpg

The one in middle is learnt to come as standard on the Sport.jpg

Fit and finish

The other no less critical factors that, to my mind, work to make the Sport into a fine shooter are the finely worked out tolerances inside the powerplant, as well as a visibly improved material grade and workmanship. Just look at the quality of the material and finish of the end block, the exact fit of the spring inside the piston, as some examples. Look at the shining finish inside the wiped compression chamber in the photo. The material, finish and steel temper of the piston is in stark contrast to those used on all the famous old ARs of SDB.
I was further impressed by how its designers would have worked on the weights of each of these individual components (they all weigh and size up differently than their predecessors!...so no easy swapping!) to make the overall balance and weight of the gun so hands-on in the shooter’s hands! You will also not miss to notice the neoprene seals (piston and breech), the star washers in the stock screws….as some welcome yet standard features.

With that kind of a fit, you would likely have a straight shooting behaviour.jpg[/attachment]

My spare piston (with the top guide) could give one mm more of stroke.jpg

Non-latex nitriles are good when working with chemicals.jpg

Pretty evenly worked out CB for a 130mm spring room.jpg

Where are the nicks?

1. The spring first! I learn that the new lot Sport is going to carry a newly developed spring (I could get one as a spare to try myself….the one you see on the left of the scale in the photo). My gun though came fitted with a previous spec spring (the one on the right side!). My tests confirm a much better modulus of rigidity in the new spring. What you see in the photo is a fully set free length as I have already set it up for deployment, and am raring to try it out once my gun settles down fully.

2. The drenching lube inside the action: Just see some of the photos of the stock gun being disassembled …and if you were the production in-charge, you will have fired your floor manager on charges of wastefulness. [Too much of lube can also significantly hasten damage to seals, by the way!] I mean who needs that much of precious moly embedded lube? You heard it right. The lube inside the action is not 40Wgrade oil, but a good quality CV grease with Molybdenum Disulphide; not sure of the Mo2S percentage though.

Piston dripping wet as it comes out of action.jpg

3. A top guide: What’s so averse about a simple top guide?...and it takes so little to install one! Wonder what’s stopping them from installing a top hat. I turn my own in various material, and none of my guns run without one. The little thing can be so handy to manage piston weights, some preload, ..of course besides keeping the spring straight and helping easier torque. [A little innovative application with DIY tools is good help in turning tophats, seals, etc.]

A little innovative application with DIY tools is good help in turning tophats, seals.jpg

4. A better crowned muzzle would make it look real savvy!: Just take a look at the brief crowning I did at home on my 27. It does give the gun a better look…besides ensuring better protection for the rifling, of course. The crown I did on my 27 looks far suave than the Sport's bland pout.jpg[/attachment]

5. Please use Low torque spanners to fix the barrel pivot screw: And may be also a couple of barrel washers on either would be a useful addition, and lessen wear on the base block sides and the action fork insides. [If you are ham fisted, you would likely end up defacing the screw head in your attempt to open it. Using proper solvents is advised.]

Opening the barrel screw needed special solvents.jpg

Parting words…

Most of us, including those on this forum, are basically just shooters /plinkers; A handful, at best, can be called fitters (what you commonly, and erroneously if you like, call ‘tuners’)…and may be just a couple would be into tuning air rifles. So, for all you shooters and power buffs…those photos of the gun’s groupings and the ME figures improving by the day as it is settling down should be more than any number of words in favour of the gun. You can pick it up and do three things –shoot, shoot and shoot. That incidentally is a great way to burn all the extra lube…shooting /plinking pleasure comes as a bonus here! Just a couple words here:

• I believe that in its current state the gun would do best with tight fit, higher start pressure pellets. Mine shoots best with Precipell 8.7 and 9.6.
• Resting the gun muzzle-down should be a useful practice.
• Keep an open eye for changes in smoke, shift in POI and ME, say every 200 shots or so. Should tell you when your gun is settled.

For the rest of us, open the gun (because you will keep itching until you did that!)….just wipe clean, reassemble and shoot. Instead of a thousand shots, you will, like me, have a settled one by 50 to 100 shots. Also, if you were me, put a top guide with no more than 10 mm of lead-in for the spring. In all, adding it increased the gun’s original preload by just 3mm to 75mm.

Here's a note for all (just in case you overlooked): Notice how the gun, as it's settling down, is not only spewing less and less of smoke...but more imp, is improving its consistency (low ES) and increasing muzzle energy!! I take that as an attribute of a fine shooter settling-down (breaking-in or bedding-in, if you like please!).

I will try to keep updating on the gun as I shoot more, and try out alternative states of tune.

Best regards,
Prashant

[Rudransh]

Dear Prashant hi
I think it's most detailed review or write up I have seen in so many years of airguniing.A real world gun with real world pellet giving astonishing fpe and the price of sdb are unbeatable.
Recently I too found that internals are polished in my magnums.so it's a good sign but due to over lubing man I always had to open it and wipe out extra lube so u too confirm my experience of over lubing.God give them some sense of lubing.
In addition I had to put sleeve into my magnum to tame it's recoil at that power level and yes it's full 14 plusfpe giving first Indian made airrifle.

I think Prechihole should come with some decently powerful airrifles soon as we know our legal limit now. Which 20 joules otherwise soon sdb will shift position in ranking.
We are lucky to see and feel this evolution of airrifles.
Regards
Veerbhadra

[Basu]

Dear Prashant ,
This is a very comprehensive Airgun review in recent time.
You have expressed maximum , the words could reach.
I am deeply irritated having seen the colour of stock seal.It is simply lack of of minimum understanding of airgunning.The excessive use Moly & dieseling killed the seal before setting.
It is clear that SDB loves to stay in 50s not 2018.
The unique feature of Sport is it's convertiblity.
One can use it as target rifle & also as sport rifle by varying the preload.
I have been rating this gun high always as value for money.
I am little surprised to see that your gun weighs 200 gms more than my Sport.
It is nice to note that as compare to 5 years back , today customer has more options to choose.
Waiting for another critical review once gun is settled.

Basu

[Gunner_dh]

Now, that we call a review. Basu da I believe is more than delighted
I have been also thinking on adding this beauty to my stock, hopefully will get it in recently.

Just one question though, rather two.

What is FPE of Sports with the new Spring?
Is SDB still not installing the new spring in their Sports?

Regards
dh

[ashwin1627]

Dear Prashanth,

On word for your article "MIGHTY".
It's been a pleasure to read such a illustrative aritcle about the SDB sport.
Thanks for this great piece of information.

Regards
Ashwin.

Sent from my ONEPLUS A5000 using Tapatalk

[prashantjha19]

Dear Prashant hi
I think it's most detailed review or write up I have seen in so many years of airguniing.A real world gun with real world pellet giving astonishing fpe and the price of sdb are unbeatable.
Recently I too found that internals are polished in my magnums.so it's a good sign but due to over lubing man I always had to open it and wipe out extra lube so u too confirm my experience of over lubing.God give them some sense of lubing.
In addition I had to put sleeve into my magnum to tame it's recoil at that power level and yes it's full 14 plusfpe giving first Indian made airrifle.

I think Prechihole should come with some decently powerful airrifles soon as we know our legal limit now. Which 20 joules otherwise soon sdb will shift position in ranking.
We are lucky to see and feel this evolution of airrifles.
Regards
Veerbhadra

Dear Veer,Thanks for your kind words indeed...glad you liked the post!

I did try a sleeve in the Sport during reassembly. Obviously it had to be very thin given the already snug fitting spring. I felt tentative pushing the spring in with the sleeve....and soon decided to take it out for the time being lest it impedes spring energy more than just a bit, which would otherwise be acceptable. But that surely is a worthy suggestion for all.

I feel you should also share about how the "legal power limit" evolved to 20J for us here in India....for the benefit of the forum members.
As for the competition catching up, sooner our Precihole folks come up with a 20J air rifle, the better for all of us! That I learn is gonna be a longer stroke gun (I personally prefer longer stroke ones and have a personal taste for their easy firing cycles).

And last but not the least, when are we seeing a review of the SDB Magnum please??
Regards,
Prashant

Added in 31 minutes 29 seconds:

Dear Prashant ,
This is a very comprehensive Airgun review in recent time.
You have expressed maximum , the words could reach.
I am deeply irritated having seen the colour of stock seal.It is simply lack of of minimum understanding of airgunning.The excessive use Moly & dieseling killed the seal before setting.
It is clear that SDB loves to stay in 50s not 2018.
The unique feature of Sport is it's convertiblity.
One can use it as target rifle & also as sport rifle by varying the preload.
I have been rating this gun high always as value for money.
I am little surprised to see that your gun weighs 200 gms more than my Sport.
It is nice to note that as compare to 5 years back , today customer has more options to choose.
Waiting for another critical review once gun is settled.

Basu

Dear Basu Da,
So much value the word of encouragement from you! Thanks so much.
Here's a secret: It was actually your opinion and feeds on this gun that got me in....I always felt reassured going for it.

And you are right about the over-lubing issue. It ought to be addressed forthwith by SDB. A simple comparison with my current spec Model 27 (which is almost the same stroke as the Sport) tells you that they have shot the SCR up by 50%. That's a huge change....especially also when you factor in the higher rate spring used in the Sport. In all, a perfect recipe for a high peak pressure and temp. And if anything, it only calls for doing everything possible to avoid dieseling in the action.
The SDB folks, on the contrary, provided for more than enough of it with that generous lubing though! I find it hard to believe that they would be ignorant of such a simple and obvious thing as this. If anything, I think their production floor guys are just simply oblivious, or are careless.

By the way, I have kind of tried to file the original seal somewhat even and restore it. Pretty battered it is, but seems to somewhat retain some of its character. If I ever need to check performance with a loose fit seal, I will give this one a chance and check.

And yes, there is loads of other info on its design and behaviour that we will get to see in the coming posts ...and as the gun settles. I avoided over-loading the first post with these pieces of info lest it became content heavy.
Regards,
Prashant.

Added in 24 minutes 49 seconds:

Now, that we call a review. Basu da I believe is more than delighted
I have been also thinking on adding this beauty to my stock, hopefully will get it in recently.

Just one question though, rather two.

What is FPE of Sports with the new Spring?
Is SDB still not installing the new spring in their Sports?

Regards
dh

Hi DH,
Glad you found the post of interest!
You any way know enough about the gun for me to be speaking in its favour. As I said in the original post, it serves its name rather well -SPORT! I personally felt it feels and behaves like a handy sporter.

I am yet to test the new spring so no confirmation on the fpe. I should wait for the internals to have a good run-in before trying it out. However, going by my calculations, the new spring's stiffness is some 22% lower than my stock spring, ...but it would offer some 7% more of natural preload. So, some tweaking with the preload may finally help even out the spring energy. Much also depends on how the spring behaves in a certain preload and stroke set up -in all, a combination of the wire alloy, quality of tempering, tensile evenness, and so on. The new spring definitely looks and behaves much-much consistent than the older one so far in my fiddling with it. No wonder, SDB have opted for it.

I think SDB folks could sound us out when they commission the new spring in the gun.
Regards,
Prashant

Added in 11 minutes 13 seconds:

Dear Prashanth,

On word for your article "MIGHTY".
It's been a pleasure to read such a illustrative aritcle about the SDB sport.
Thanks for this great piece of information.

Regards
Ashwin.

Sent from my ONEPLUS A5000 using Tapatalk

Hi Ashwin,
Trust you have a taste for journalistic accounts (as against point-to-point ones) ...reason why the post pleased you. Much delighted it was of interest, and the fact that you cared to revert. Appreciate it!
Do also share about what fascinates you more wrt air rifles?? so more people can chip in to keep folks like you delighted and interested here please!
Take good care.
Regards,
Prashant

[Maroon_d3vil]

Master stroke by prashant ji! Such a pleasure reading a detailed and well illustrated review after a long time.With your awesome tuning skills, you will definitely bring the most out of this AR.
And yes, congrats for the new beauty prashant ji!

Regards,
Maroon_d3vil

[prashantjha19]

Master stroke by prashant ji! Such a pleasure reading a detailed and well illustrated review after a long time.With your awesome tuning skills, you will definitely bring the most out of this AR.
And yes, congrats for the new beauty prashant ji!

Regards,
Maroon_d3vil

Long time, dear Maroon_D3vil! Hope your Precihole guns are doing great! Do tell us how the new NX has been doing.

As for tuning the Sport, ...well, that should be part of the game, you are right. And for the benefit of all others who may be contemplating getting this gun, here are a few top-of-the-mind hunches I feel like sharing (more like prelim alerts!!...not confirmed facts yet!):
1. I have not seen its .22 cousin. However, from some of what I could gather from writings of members here and elsewhere, I feel that we should NOT expect the current .177 version to be as smooth a shooter as its .22 counterpart; especially if you insist on keeping it at or around 12fpe power. The reasons are far too obvious: You will need a far heavier piston assembly and a much stiffer spring in a .177 set up to match the .22 ME figures. And when you do this, the shot cycle feel ought to be quicker, snappier, and unfortunately also, harsher.
That is much like how the gun is shooting currently.
Do I like the feel?? I am beginning to have second thoughts actually.
My gut is, the .177 Sport should shoot smooth at around 10fpe, give or take half fpe. That would suit its caliber,weight and profile most snugly, I feel.....and also ensure better life for the seals, spring, etc. [I have noted the very high compression ratio and its tell-tale effect on the seal in the original post.] I am also noticing that the breech seal may already be giving in.
The current spring surely looks like an overkill. Add to it a high sectional density piston weighing 240gms against a cross sectional dia of just 25mm.....You really have very high momentum going, dont you!
No wonder SDB is said to be replacing the spring already.

More on these later.... Thanks to Maroon-d3vil who pricked me to share some of my topline hunches on what to realistically expect from this gun, and where may be some prospects for tuning, etc.

Will love to hear your thoughts please!
Best regards,
Prashant

[prashantjha19]

Two other Tunes for the Sport

Hi there!! In this post, we will look at two different states of tune I tried on my Sport in these past couple weeks. Those of you looking to tweak your gun’s specs could find some of it useful.

My Sports's pellet preference continues.jpg

My Sports's pellet preference continues

Good accuracy, but only with its preferred pellet.jpg

Good accuracy, but only with its preferred pellet
The post is advised only for those with serious inclination into air rifle tuning….so casual readers would kindly ignore the dense, and sometimes technical, nature of the post please.

Despite its sharp shot cycle, Sport shoots more accurately in the real world, sporting hold.jpg

Some would ask, “why alter” the gun at all?” Here’s why I did it…

1. The scorched state of the seal coming out of the factory set up was a cause for worry. Of course, an abundantly overflowing lube in the action was a prime reason for this (rather than only the stiff set up)…as we will find out soon! De-lubing and installing a new seal in the last re-fit did eliminate dieseling…well almost. Incidentally, the old scorched seal retains its shape and tenacity; and so I decided to go with it in the new setups.

Careful filing of the old, stock, scorched seal brings it back to life.jpg

And, as the next disassembly confirmed, cutting out the supply of lubes ensures an almost-new-look seal post 400 shots despite high peak pressure and temp.

Seal comes out fresh from a non-lubed action post some 400 shots.jpg

2. Look at how the poor breech seal was being punished on each shot.

The seal's bottom would get squeezed in on every shot.jpg

While the neoprene breech seal supplied with the gun is soft, pliable and yet sturdy, I had no doubt that the peak pressure inside the action was way too high for this lofty little power plant. On each shot, the blast of air would squeeze the bottom of the seal into the seal groove. Fearing possible leak on the next shot, I would scoop it up back with a soft pin, etc. (It soon ended up tearing the poor thing!) I had to try several seals (o-rings, leather, neoprene), and with varying elevations, too.

Try out as many options while seeking a perfect breech seal fit.jpg

Sadly, none lasted beyond a couple dozen shots each. The cracking sharp shot sound only confirmed a very high peak pressure even though I had mostly taken care of dieseling by clearing all extra lube. ME in any case remained way up at above 11.5flb across pellets.

Precihole's o'ring seal sits perfect in Sport if you can find the right padding.jpg

3. I had already shared my sense of discomfort with the original specs – where a very high preload had skewed the spring energy breakup (between piston energy and preload energy) –and made only a tad over 76% available to the piston. That is really poor; and I was most uncomfortable about this tune! In my tuning assignments, I aspire for a near 90% share for the piston. Difficult to achieve in Indian ARs, but no harm in aiming high!
In this tune of my Sport, clearly either the stiffness of the current spring or its free length was not suited to its power plant. My thumb rule, based on my humble understanding of airgun action designs and states of tune, is to pick springs that offer a preload ideally in the range of 40-60mm. Remember, we hardly have great quality spring wires (unlike the West), nor are the transfer posts on most Indian airguns are of efficient dimensions. Next I decide on what stiffness of the spring I need, which of course will be a factor of its WD and CD, which in turn will be dictated by what room the piston allows, and so on and so forth. Key factors that make selecting an ideal spring for your AR a tricky business! So, here we go…

Tune 1: Trying out a Soft tune first!

All in all, those are mostly what pushed me to alter my Sport. As Sport is a close kin of the Model27, I was keen to see how it behaved in a soft configuration that my 27 is in currently (my Mod27 delivers 8.5flb with a heavy, low start pressure pellet with fine accuracy). Replacing the Sport’s stock spring with the standard, soft Precihole spring reduced the natural preload from 75mm to 60mm. Reason why I picked the spring in the first place. (Of course I sleeved the piston to eat up the 1.5mm of slack inside.)

Left -Seal comes fresh post 400 shots. No lube help! Right -PH spring with a thick sleeve and old seal on the spare piston..jpg

Lower preload, coupled with the low rate (stiffness) of the new spring, reduced the piston energy by some 77% at 29.62flb. That incidentally, as tuners and designers will acknowledge, is what is available to the piston in a standard UK-spec LGV with 88mm stroke and makes it close to 40% energy efficient. Even more importantly, this piston energy in my Sport, at over 81% of the total spring energy, was way better than the mere 76% made available in the stock config. We know for sure that a good shot cycle behaviour coupled with more of the spring energy getting invested in the piston (as against that expended in preload to contain piston bounce) characterizes an energy efficient action.
So, is the Sport efficient in this soft setup? It isn’t, I am afraid. Well, I am not trying to compare this 78mm stroke with the 88mm of the LGV; but I sure aspire for 33-35% efficiency. So what if it’s a .177 cal? I am convinced it is pretty achievable….only if one knows how…as we will soon see in the next tune!
With this 5.2N/mm spring and 60mm preload, my gun delivered an ME in the range of 7 to 8.3flb across different pellets. As you can clearly see, it is way less than even 28% efficiency.

Increased vibes and recoil intensifies the gun's pellet fussyness.jpg

Not so great groups in the photos is my way of telling you that recoil and vibration on each shot was too palpable to be missed. Airguns can “prefer” one or more pellets; but that should not mean they can be so way off with other pellets. If they are, then there’s something amiss. In the current state of my Sport’s tune, what this means is –one, air flow through the TP was choking early in the compression stroke, resulting in early piston bounce; two, the soft spring despite sufficient preload is unable to contain the bounce of the heavy piston efficiently. The set up and behaviour is so amusingly close to what I had in my VX100 stock set up. (If you have read that thread, you know how installing a barely stiffer spring with a fair bit of preload yielded in the range of 125% higher ME, fine shot cycle behaviour, and all without compromising accuracy.)

The fork and TP dimensions of the Sport (right) are different than my Mod27.jpg

My Sport’s SCR is 50% more than that of my Mod27. My spreadsheet, practically accounting for all nooks and crevices in the compression tube to work out the lost volume, calculates the SCR at 313:1 for the Sport’s 17mm x 2.7mm TP. This + its heavier piston assembly + the smaller bore dia (read high sectional density) + the use of an easy fit synthetic piston seal, together definitely ask for a stiffer spring (read higher momentum)! In simple terms, what is happening is that post mass air flow choking at Mach1, more of the KE (thermal energy) of the compressed air is being lost in driving piston bounce rather than getting transferred to the pellet. That is something not desirable!

The only other alternative here with this soft spring was to increase preload further. But with less than 125mm spring room available in the action (my tophat and couple thrust washers took some 5mm off the standard 130mm room available in Sport), and the PH spring going coil bound at 120mm, this got ruled out. I could cut off some coils, and try this option out though; but I didn’t feel confident it would take the ME significantly high. But that’s just my gut! I do however get a sense that it could give a sharp, snappier and stable (low recoil) shot cycle. But as they say, you are never sure with airguns until you have tried it out. And so, someday I will use a shortened PH spring in Sport, too. For now, I am too impatient to get the gun blazing in a stiffer set up….and hence the next tune below. I am saying this all the more because peak temp, comp ratio and pressure calculations for this tune are pretty decent….a wee bit above it should be for mid-range ARs – 1248*C, 36.69:1 and 155 BAR, respectively.

The breech seal behaviour continued to be erratic. And so, I finally went for the old, tried and tested option –cut an oversized leather seal, soaked it well, lightly hammered it in and left it with breech closed overnight. Job done! That’s how it stays here on. I hope SDB looks into this breech seal issue please.

Tune 2: A Stiff, optimised FL stock spring …for a Rock solid shot feel!

Yup…that’s exactly what occurred to my mind on the very first shot of this new tune. The very first trial shot after the tune up pierced through the steel of my old electricity meter box target holder at 7 meters.

Through steel at 7 mtrs -First pellet post tune.jpg

Let me admit first that I was keen on sticking with the stock spring. My calculations of its stiffness (5.91N/mm for standard spring) as also its overall dimensions and behaviour were generally boding well. In addition, please recall the fine fit of the spring inside the piston. It is sized rather perfectly. Not for nothing manufacturers pick a component in a certain specific dimension. In any case, I do not favour altering original specs of any gun way too off, unless there’s a pressing need.

3 rings cut, end coils closed and ground flat.jpg

My spreadsheet confirmed to me that cutting just three rings (two active gaps) would increase the spring’s rate by 2pound force to 35.8lbf (6.27N/mm), and yet would bring down its free length to offer a preload of 55mm. In this set up (with 5mm less of preload), the preload energy would remain almost the same as was with the softer Precihole spring (6.9flb). However, this resized 6.29N/mm spring (fewer coils increase the rate from 5.91 to 6.29N/mm) will apportion 83% of its energy to the piston at cocking, which would be 33.9flb. 83% break up is decent….and I decided to go for it. My consultations with enlightened minds like Basu Da on this forum on the subject told me I was on the right track.

In addition, a word of appreciation especially for SDB’s decision to go with the smaller bore actions in their new breed of guns by no less a mind than Dr. Shirsat (of Precihole) in a private consultation encouraged me to continue applying myself on this gun, and my quest to refine its shot behaviour and output.

In the end, I am so gleefully pleased I went for it. In the tests, the sheer feel of the shot cycle, the crack of the shot sound, the solid, no-time-lapse impact at the target…. left nothing to be verified further.

So much more stable and accomodative of different pellets in the new tune.jpg

I did casually chrony the gun, and all pellets were delivering beyond 11fpe. Will do a detailed chrony once I get some time to shoot it enough and settle the gun down. But, just to confirm if I wasn’t too excitedly overwhelmed, I carried my freshly refitted gun one day to the rifle club where my child practices for the state shooting championships. I let seasoned shots shoot the gun …. Their amused faces and the tight groups at 10mtrs told me to go ahead and pat myself. One more thing –My 14 year child said its cocking effort was just like her favourite VX100 (which is running at over 10fpe currently). I missed to measure it yet, but compared to the original over 11kg cocking effort of the stock gun, in this tune it wouldn’t be any more than 9.5kgs.

Sport's group (on right) convinced me to reduce recoil on my child's VX100 (on the left).jpg

I am no good shot, but my casual plinking groups with the VX and the Sport (in the photo) convinced me that I had to reduce the recoil of the VX100 which my child is shooting in the state championships 10mtr OS Youth category event this month. [That was a cake walk …just replacing the original steel top hat with a DIY polymer one made her VX100 so pleasant. I will be updating the ME and groups of my lighter-piston VX100 on this other thread -“Precihole’s VX100: An Alternative state of tune”. Please check it out on

I will soon update the post with ME figures and groups of the Sport in the new tune with different pellets.
Till then, please take good care and shoot responsibly!
Best regards,
Prashant

[Basu]

Dear Prashant,
Excessive air pressure pushes the breech seal down into the groove.
The solution is to pull the seal by using hair pin.
Fill the lower gap with cotton thread and put back the seal as it was.
My all seals are intact in Sport even after fierce power 12+ ft lbs and after dieseling induced power output of 18 + ft lbs.
This metarial has very high resilience.

Went through your post. It demands re reading.
Such detail analysis ,will make Tom Gaylard aka B B Pilletier envious.
I wish if he could ever see your posts.
Not joking.......

Basu

[prashantjha19]

A kind man always wishes good!! Thank you, Basu da!...but folks like me are too small to link up with the likes of Tom G, I know.
I sure have learned a great deal from his likes indeed, and so gratefully, of course.

Honestly, I know most people are wary of what I write, the details I share, etc.; and that most suck up only very little of these (if at all, that is!). Even then, I insist on including at least the basic tech details as and when I feel it warrants. And this is because these constitute an important aspect of the gun's reality. I share in the belief that interested minds will someday see value in some of these details....even if they do not for now.

I strongly feel that we all have a duty to contribute our little bits to the sport of airgunning in India. That is one way we could take it to a different league in our country. As many of you repeatedly keep emhasizing, airgunning is much more than just hunting, or plinking, or target shooting, or can-busting. There indeed is so much that makes them shoot and behave the way each one does. What are those facets...is what people ought to appreciate, too (not saying, they all become masters of it!).
Really, we are so much lagging behind in how our folks approach and deal with airgunning in general (barring a small fraternity of few passionate ones and connoisseurs, that is!).

And finally, your suggestion about shimming the breech groove for the seal is very well noted and taken! Why didn't it occur to me earlier, I wonder! The quality of the seal material is sure good, as I have noted, too. It's its fit that came up as an issue with me. I understand that you, Veerbhadra, and others have happily been using the same one for several thousand of shots on your SDBs.
Thank you again and my best regards,
Prashant

[sagar 12345]

i am very happy when i read your report on sdb sport.recently few days before i recived my sdb sport in 0.177 cal.as basuda said it has solid punch & power as compare to my artemis i feel. since i am new to this shooting game i dont understand some technical terms like scr piston energy so i read this article again & again .every time i read it i enjoy it.please make an article on sdb sport how to make this gun smooth.after around 400 shots i also want to open the sport & clean it & use some precihole moly. but i had faced problem in fitting the trigger on artemis . it is not easy for me to allign the holes of trigger & tube to insert trigger pin it.i did not face any problem with breach seal neoprene breach seal is intact & it did not change its shape after 400 shots i use usrh & usfh pellets & i got very good accuracy.this gun is very different from other due to low weight & high me.thank you for this beautiful revive on sport.

[prashantjha19]

Hi Sagar12345,
Wonderful to see your interest in AR mechanics and functioning!

First thing first...How to lube, smoothen and refit your Sport smooth:
I am assuming you have the necessary basic tools and contraptions to work on, dis-assemble and reassemble ARs. If you don't, do get one, esp a sash clamp.

Here are a few handy tips for all beginners:
1. Please add a couple of wheel spokes (those of bicycle, tricycle rickshaw, and mobike) to your tool kit. They prove to be handy multi-taskers -as cleaning extensions, as punch pins, as hole stoppers...and can give you access to some unreachable nooks inside piston, tube, etc.

2. Trigger block installation: Loosen the adjust screw as far as you can; and when you do this, it would be a good practice to do it by half turns counting the number of turns you make. It comes in handy after refit ...when you can tighten it back by as many turns and you have the same load trigger back in the new set up. No guessworks! (You can even even remove this adjust screw completely when you become adept at disassembling soon!).
You are facing problem in fixing the trigger back (aligning the holes) because your adjust screw is pushing it ahead.

3. As for refitting your Sport, after you open the gun,....all you need to do is wipe all lube off, Add a very thin synthetic sleeve inside the piston (and over the guide if needed); Install a lightweight poly top hat for the piston (if you can turn one yourself)....and just reassemble. Job done!

4. Shoot plenty....and soon you will know (based on the shot cycle feel) if you want to do any other changes (such as replace, scragg or resize your spring, or reduce piston weight, alter stroke, etc.)
But mostly, you wont need to do any of that.

And pls do not get bogged down by the tech terms....you will become familiar with them the more you use, read about and converse ARs!!
Just so you asked....SCR is static comp ratio (ratio between swept vol and lost volume). For a gun with the current Sport specs, you generally
want to keep it in the 350:1 range.

Piston energy is simply the KE imparted to the piston by the spring so it can effectively compress the air in the comp tube upon being released (When you start understanding spring mechanics, springer behaviour will be easy to figure out). Here's some basic bits for all beginners (Just to get a basic sense ....pls do not let any of it confuse you though...).
You do NOT NEED to know these...but if you do, your inferences from the way your gun behaves will be much more informed, and you will feel confident about altering any of its specs.

The sudden compression of volume of the available air in the comp tube results in increasing the momentum of air molecules exponentially. It is this momentum that is at the heart of all ME (whether springer or PCP). And, as we all know, the KE of air molecule is nothing but the temperature of air (Kelvin). Consequently therefore, the temp inside the comp tube shoots up by hundreds of centigrades (of course, only for a couple milliseconds). You will hear terms like peak temp, pressure and comp ratio, etc.

Here on, the energy (KE) of the molecules in translational motion (and not of those in vibrational or rotational motions) gets transferred through the TP to the pellet.....which, sitting in the breech, resists being pushed (you will hear terms like pellet start pressure in this regard). When it does move, the rush of air through the TP (we call mass air flow) is so huge that it soon reaches the MACH1 level (the speed of sound). This level is very critical in determining the shot cycle, as that's when the mass air flow through the TP chokes (which is when the energy utilization of the remaining compressed air gets reversed, i.e. it is now used to drive piston bounce, rather than for pushing the pellet).

Now, MACH1 velocity is a direct function of the temperature....The rise in temperature raises the MACH1 velocity significantly [20 times the square root of temp in K (Degree Centigrade+273]. And because the compression has raised the temp very high in the action, this temp becomes very crucial to deciding WHICH stage of the compression stroke the piston will bounce.....or simply put, in determining the length of the ACTUAL compression stroke. Please remember, the actual stroke of a springer shot cycle is not exactly what we measure physically, i.e. the potential stroke. Its a tad less (else there will be a damaging slam of the seal/piston on the cylinder wall on each shot.

From the point of time when the pellet starts to move and the TP chokes (and piston bounce commences), the piston and the pellet are moving in the same direction. This phase (termed as the cylinder pulse) is THE most important phase ....as this when the pellet attains most of its energy. Naturally you want to keep it long (again, we are talking only in terms of some milliseconds here, too). Reason why longer stroke actions have a smooth behaviour with good ME (all other things being equal).

So, now you also know why pellets of varying profiles behave so differently, many-a-times, being quite deviant vis-a-vis the others. Their fit, finish, shape, weight decide not just their acceleration profile in a given barrel, but also at which point of the comp stroke will they start moving (in a given tune of a springer)....thus affecting the point of piston bounce and how much KE of the compressed air are they able to consume effectively.

Next time a pellet behaves differently (or your shot cycle feels awkward) you would have somewhat of a fair idea of what MIGHT possibly be causing it!
That is all is the purpose of sharing this BORING piece of info above.....but If it helps even one guy, I would have been served well! So much for now..
Best regards,
Prashant

[sagar 12345]

thank you very much sir for so quick reply. as per your guidelines i will disassemble the sport & just wipe out extra lube & use some precihole moly & asseble it again . i will share the behaviour of sport after that. once again thanks for sharing valuable information .

Added in 2 hours 49 minutes 54 seconds:
sir can you tell me about role of top hat in rifle. how to make synthetic material top hat . sdb did not sell top hat .i search online no one sell top hat so please tell me how we can make top hat for sport or any other air rifle i also have artemis, gennex & ph club elite & huricane mod 16 all in 0.177 cal.in artemis i replace stock spring with precihole full spring of 40 coils . it is very difficult to reassemble artemis because ph spring is long than stock spring of artemis but i mannaged it .now artemis shoots smoothly but it did not give me power claimed by company so i bought new original spring from kolkatta dealer but i did not change it .because precihole spring gives good accuracy.i did all these changes with out any technical knowledge but just on basis of avaibility of spares.i have spring compressor , precihole moly, wooden rod for cleaning compression tube.

[prashantjha19]

Dear Sagar12345,
A properly sized top spring guide (usually termed top hat) provides a secure anchor to the front of the spring...+ it helps keep the spring straight during compression. Additionally, it is also handy in managing piston assembly weight.
The best option for you would be to use the Precihole guides -both top and rear guides can be turned to fit into the SDBs. For the steel top guide, you will need a lathe to drill a 10mm oversize hole so it can slide into the piston shaft of SDB guns. The poly rear guides you can cut and mend yourself to slide into your pistons.
I always use a pair of thin steel slip washers with Moly over all such guides to ensure easy torque for the spring.
Best,
Prashant