Increasing the velocity of your air rifle - possible?

[narach93]

Pashantji. Thanks for your kind and encouragement words. I am trying to explain your query through a sketch. Pl have a look.

Added in 32 minutes 24 seconds:

indiansforairguns_2.jpg

[prashantjha19]

Dear Prashant,
To answer your question, I reassembled my Precihole pegasus with already used gsmith 27 spring. I have avoided extra preload given by spring top hat because I broke one new gsmith 27 spring with it. I have shot around 200 pellets, though not thousands. Five shot group (12 meters at sitting position) with Precipell field target (older gsmith manufactured, 8.32 grains) is attached. Recoil has reduced a lot and it seems to be accurate.

FPS values are 778, 805, 794; average = 792; FPE = 11.59 ft. lb. or 15.72 J.

Very impressive results, Dear Master!! ....both on accuracy and power!!
Many thanks for sharing your experiments. It helped me learn a lot. Will try my hand and report in due course. I am sure you did fit in some kind of a thrust washer (howsomuch thin) in place of the top-hat (unless of course you had a super fine spring face).
Thank you once again. Really appreciate.
Warm regards,
Prashant

Added in 9 minutes 1 second:

Pashantji. Thanks for your kind and encouragement words. I am trying to explain your query through a sketch. Pl have a look.

Added in 32 minutes 24 seconds:
indiansforairguns_2.jpg

My dear Narach93,

I really do not have enough words for thanking you for taking the pains to communicate the details to us. I am so sincerely and earnestly appreciative of your kindness. God Bless you!!

And BTW, I have become a terrific admirer of the out-of-box thinking you are capable of......You have such a keen eye to locate otherwise mundane and ordinary things like sprayer washers that will serve our airgunning requirements. Hats off!!
I am surely going to copy this.....so much also as my true gesture of gratitude for your help.

Keep smiling!
So much appreciate!!
Best regards,
Prashant

[Basu]

Dear Master,
Have you Put the stock top hat in Pegesus with Gsmith 27 spring.

Basu

[Master]

Dear Master,
Have you Put the stock top hat in Pegesus with Gsmith 27 spring.

Basu

No, stock top had to be removed. I did not use any shim or washer in front of spring. Is it required ? Gsmith springs are, I think, sufficiently smooth at the ends.

Gsmith 27 spring with stock top hat resulted in too much stress on the spring and it broke after 15-20 shots. Before breaking some fps results are as follows:
gsmith high speed (9.9 gr): 702, 693, 678 => 10.17 ft. lb.
gamo hunter (7.56 gr): 862, 853, 880, 876 => 12.71 ft. lb.

[Basu]

Dear Master,
My theory does not approve to use tophat at this stage of power.
The spring really helped to boost power.
Normally the stock spring delivers 9.5 fpe.
Here your grouping suggests that there was no much big trade off between power & accuracy.
My Sport reaches 12 fpe at ease and with Unitedshot PH 8.4 gns , it hits 14 fpe.This is too much for Sport but there is a trade off.

Basu

[narach93]

Prashantji. Thanks for your kind words. I am placing image of springs which speaks for themselves as the source of power .

Added in 27 minutes 51 seconds:
These two images tries to show a very basic comparasion in terms of number of coils and length of springs. Pl try to read the names of the coils (sorry for the small letters). It may be a crude way to describe the source of power. I have used all these springs and measured their power through old monoroma yearbook penetration method. Vortek is supreme followed by diana, cherokee, Gsmith, National and precihole. As far as smoothness concerned, precihole rides higher than everyone but very close to vortek.

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Wish you all very happy diwali.

Added in 7 minutes 1 second:
Pl help me getting a simple chrony which finds much recognition in our forum. I will be grateful.

[prashantjha19]

Dear Narach93, Thank you so much, yet again!. Those are very informative photographs indeed. For the life of me I wouldn't have known wht a Weihrauch or Diana or Vortek kit of spring looks Like....but for your kind sharing!! I am yet to get over our very own Cherokees, PH and G Smith stuffs.

Just to flag for you all - DO you all scragg your springs before installing? I know Basu da usually does.
Only last night, I opened up my SDB Classic 45. The stock spring measured 28.5 cm, but is slightly canted. I checked a Cherokee 27 spring (as advised by Basu Da in an earlier post). It fits the guide snugly. So I planned to try it out. The spring was 31.5 cm in length. Scragged it in my bolt unit overnight. After seven hours, its length was 28.5 cm. Is also certainly more stable and dependable to go with.

Out of curiosity, I once again scragged the old stock spring for 2 and a half hours. Lo and behold....it remained at 28.5 cm. [By the way, I had scagged the stock spring a month back right inside the receiver by leaving it cocked for 5 hours.

Just trying to emphasize that scragging a new spring turns out to be a regimen worth doing for all tuners.
Also, I will be trying out on this tuning exercise some of the tricks (washers and sleeves) I learned so gratefully from you and Basu Da!!

@ Dear Master, just wondering, do you think your first G Smith spring breaking apart after 20 shots had something to do with scragging (or not scragging)?? Of course, the high preload must have been a predominant factor, I understand.

Happy Diwali to all! God Bless!!
Prashant

[Maroon_d3vil]

A brilliant thread and very nice contribution by respected members. Special thanks to @narach93 for the sketch and spring comparison. I have bookmarked this thread. Happy Diwali everyone!

Regards,
Maroon_d3vil

[Basu]

Scragging is sometimes called as preset.
You are lucky to have a Cherokee which did not break after nut bolt scragging.
Cherokee in SDB 45 may be counter productive as it may contribute to piston bounce.
45 may max deliver 10.5 fpe even after best tuning.
I only punish a spring by scragging it for hours when I observe that the gun is hitting everywhere except centre.
Believe it or not , I got max power out of 45 with the softer spring only.
A 6-7% decrease in free length after scragging goes to prove that it has the nice capacity to store energy for longer period.
Tirtha RIP of TTI had given me a full power spring which had free length of 30 cms, ID 13 mm, Wire dia 3.2 mm.
After 5000 shots it had a length of 28 cms.And I was fed up with it's power so replaced it.
To make 45 free of transverse vibes , you may use two layers of x-ray film as sleeves.Never forget to anchor the sleeve with a thrust washer .However the number of sleeve to be decided on the basis of difference between OD & ID of spring & Piston.
The Cherokee does not have square end.you need to grind the ends properly.
Too tight guide may reduce energy output.
Stock spring also found good in terms of lost length.
Do you use synthetic piston seal ?

Basu

[narach93]

Thanks Prashanji and maroonji. I am happy that my effort brings smile.
Dear Basu da. You are akways kind enough to share your vast knowledge on the mechanism of ARs. So much to learn from you.
Happy diwali.
Regards

[prashantjha19]

Dear all,

Sorry about getting back.....was busy servicing and tuning two of my SDB guns together - Mod 45 and Mod 65.
I tried out everything that I learnt from the likes of Basu da, Master, Sam47, Narach93, Bennedose and Briha ji all these months. Honestly, all of it were so appropriate and proved so useful. Installed the PH seal in both (with a tapered nylon washer used in the spindle of plastic water taps as the adapter on top....this little Rs.2 washer fits and works like a GEM!!).

The 45 has a 27 cm Cherokee 27 spring. The 65 goes with the 28.5 stock spring. [Note: The latter has a much easier cocking and firing feel post tuning!!] Installed strong plastic (stationary file) sleeves in both. Had to also use this sheet shim on the guide of 65 as the stock spring showed a lot of tolerance. Used nylon washers (Narach93's advice) at both ends -piston and guide (again Rs 2 ones procured from sanitary hardware store -these are used in the PVC outlet pipes for geysers!!) These fit in real good!
Of course the usual cleaning, deburring, slight cross hatching, polishing the sear and hatch, and lubing with Moly was the standard chore. And I did these at a leisurely pace -taking my time and studying each of the components closely.

Two additional things I did:
I used Silicone grease and silicone oil mix for the piston seal and head and the compression area of the receiver (instead of Moly).
I installed two small nylo-rubber washers (same as the ones used as adapter for the piston seal) on either side of the trigger block through the lock pin to contain the wobbly lateral play. It has become quiet stable now and the slight lateral play has a soft rubbery feel, and gives your trigger finger good feedback.

About the performance - Have only shot some 20 shots with each. My first reaction is: I can't believe our typical Indian guns can become so smooth. They are such a delight to shoot now. There is not an iota of any felt vibration, not the least of any twang whatsoever. Recoil, whatever would be there, is something I just fail to notice. In fact, believe it or not, it occurred to me only now when I am sitting to pen down the firing attributes. It only tells me that I had no notice of any felt recoil or thud from shooting some 20 shots each with both these guns. Good management of all the unwanted tolerances does so much wonder to a springer!!
The 45 feels stiffer than 65 (I think because of the new and touter spring).....but both are such a delight and so accurate right from the first shot. The 65 is much better than the 45 at this point.......Cocking is much much easy, and it is shooting like a dream with a .75 inch group at 17 feet at this initial stage.
The feel is so much the same I had with my PH Spartan....just that it is a bit heavier.

The 45 is shooting consistent (1 inch grouping at 17 feet) but pellets tend to land an inch or so higher than where they ideally should at this distance. Wonder if it is because of extra power. will have to check and report back later after I make some 100 or so shots. I used US 14 gr (Special pointed), MS pointed (should be some 10.6 gr I guess) and Diana shot 11.3 gr (RH) pellets. While all of these are more or less similar on accuracy attributes (Diana shot is the most accurate -its head goes in very very tight but the skirt sits most snugly at the breech). The US also seats very snug in the breach of the guns. MS is a loose fit (but on okay side).

BTW, the 65 is actually a new gun ....which went straight from the store into tuning. The couple of shots I fired at the store told me it had a very stiff cocking and a hard and unpredictable trigger. All of that is gone now.

By the 10th to 15th shot, almost no dieseling is observed in either guns. There is a slight rubbing sound at the fag end of cocking -the sound is that of the cocking shoe slightly caressing the inflated spring. However there is enough Moly on both to take care of this. Also, it should disappear after 100 cockings or so, I guess.
Just a First Report of sorts for you all please....

Also, the Cherokee I got, Basu da, had squared and nicely flattened ends. I cut out two coils and got the end squared so it seats pretty on the washers. Wire dia is some 2mm lesser than SDB's.

Will look forward to all of yours comments and further guidance. A key gain, apart from the super smooth guns, from doing this exercise myself is that it has made me so much more in sync with my guns, more familiar and confident. It is like feeling your guns, ...and not just úsing'them. Thank you all truly for all your inputs, guidance and support. Will continue needing these please....
Warm regards,
Prashant

[Basu]

Dear Prasant,
A proper tuning allows you to discover a whole new gun.
My habit has become such that i do not feel shooting a new gun , that is not smooth.
Since you have replaced the leather seal with a synthetic one, you have surely gained some 20-25 yds of extra velocity.
SDB guns respond well with tuning.
you did not mention whether or not you worked on trigger ?
the sleeves must have helped a lot to eliminate/reduce buzz or twang.
Once you feel to change the breech seal , simply opt for welding hose.
I remember , Briha , long back had supplied me those seal for my N-25 and SDB 45 and they lasted almost till eternity.

Basu

[prashantjha19]

Thanks a ton for the encouragement, Basu Da! I truly value it!

Yes, I worked a lot on the trigger...both on the sear blade and the shaft hatch face...carefully polishing the faces to align meticulously. Deliberately left some grooves on both their tops (heads) to retain some lube all the time. But the faces got a mirror finish + I also made a slight slant at the end points /release edges. (PS: While at it, I was all the time reminding myself of the 90* (minus a max of 2*) slant in the sear blade that you and Briha ji had advised long back) Lubed them nicely. And to reassure myself, I did the final TEST you advised us....cocked the guns (without pellets) and dropped several times on the bed real heavy..dropping laterally and on the butt ends just to ensure there is least or no possibility of an auto fire.
Additionally, the nylo-rubber washers in the lock pin on either side of the trigger block is proving to be a good thought. It not only almost completely dampened lateral wobble, but also there is good feedback on the finger while on aim.

And I very much remember the welding hose part, Basu Da! To tell you the fact, I have already bought and kept with me a 2' No. 8 welding hose for this purpose just after I read your advice sometime back on a thread!!

Just a correction in my last post: the target distance was 24 feet ( and not 17 mentioned earlier).

I also have two things to share with you and others please....
1. I again shot eight shots each with my two guns last night. While the Mod 65 is already shooting like a dream, the Mod 45 is a behaving erratic. With only MS pointed head, the POI seems to be in line with the POA. With others, it is tending to be wayward (say an inch at 20' distance). That's too much! The concern is that this waywardness is not consistent...sometimes to left, sometimes right, on other occasions up, etc.
It only is trying to reinforce your point, Basu da, that my Mod 45 is not comfortable with the stronger Cherokee spring.

For now, I am giving it the benefit of doubt -may be the guns (in the new hard spring) needs to settle down and bed in.
I have kept your advice right on top of my mind.....Will be testing the gun for another 50 to 100 shots to see if it settles down. If not, I will try interchanging the spring and guide sets in the two guns, and then check performance. WOuld also be a test of how the Mod 65 behaves with the Cherokee spring. I now know for sure that the earlier inconsistency in the gun was most likely due to the canted spring. This time round, we will know if this new stronger high carbon spring is also a problem that the Mod 45 finds too much to tame in.

THIS in fact should be a NEW THREAD ISSUE.....
2. Who on earth would have advised SDB folks to drill that hole on top of the barrel at the muzzle end in the Mod 65 please?? Do we know of other brands and models that have such a hole in barrel??...Do please let us all know. Apparently, it is to facilitate mounting of the foresight. (The dovetail design to slide in/mount fore sights on all their newer models (incl Mod 45) is not only neat and non-intrusive but also would be much cost effective and least irksome as it needs much less engineering and lathe works, etc.
Now, while the accuracy of Mod 65 remains sweetly consistent, my concern is - since the barrel (with all its key aspects -rifling, height and evenness of grooves and lands, consistent and parallel bore, absence of any ridges, etc.) is THE most critical factor for accuracy, HOW can someone even think of tampering with it?....and that too, the muzzle end, which IS the most vital part?? I am craving for an answer. The net did not return anything.

I am sure there must be a sound logic to it......else why would one take so much pains doing this stuff!! Do we know this logic?? Will greatly appreciate participation by members on this discussion please.

Actually, if you look at this query closely, the moot discussion point is this: With all the hell being broken loose for centuries about ensuring a perfect and seamless barrel, how is Mod 65 - with a big hole drilled transversely into its barrel just 3 cms from the muzzle end point -so terrifically accurate?? {Note: I also have a hunch that there is a slight choke in the barrel!! Please correct me..someone!! The muzzle end of the barrel is compressed into a lesser OD where the muzzle cover /shroud slides in snugly]

Will look forward to inputs please.

And finally, Basu Da, I am repeating Narach93's request to kindly advice and help us procure a reasonable crony please!! Need it all the more now...
Warm regards,
Prashant

[prashantjha19]

Hello all!
Can anyone pls confirm if SDB Model 65 barrel has a choke....or even a hint of it of some kind? Seems quite unlikely, but the design (compressed barrel OD at the Muzzle break) makes one curious.
The gun is superbly accurate (in particular with pellets that seat snug at breech - US 14 gr and 11.3 pellets in my case) ....despite the big hole drilled (just 3 cm from the muzzle end) through the top of the barrel to fix the foresight. This kind of accuracy -in spite of this hole in the barrel -is intriguing....and makes one wonder if there isn't a choke at the end!! If not, then what is it that negates the impact of such an intrusive hole??
Any thoughts..??

Added in 5 minutes 46 seconds:
Just to add,...... I also checked by pushing a pellet through the barrel; and I sensed some additional resistance at the muzzle end. Not sure if I was sensing correctly or if I was overly conscious; OR whether this resistance was due to the pellet getting a bit obstructed due to the hole ridges towards the end. Thanks, -Prashant

[narach93]

Dear Master. I have a diana 350 panther in .177. Just curious to know your feedback about the vortek PG2K kit used in your D350.
Regards