When everyone is powering up their air rifles, i thought of going the other way i,e accurate, low velocity, easy & fun to shoot product. In world of velocity crazy airgunners this might seem insane. Last November i attended a fair in my place of posting & had to open a departmental stall to demonstrate development works. In order to kill time i took a tour of that fair with my colleagues & saw a shooting stall. It was like Mecca to me & rushed to that shop to try my skills. There were 6 air rifles, balloons & tiny animal figures hanging as target. When i lifted the gun i was shocked by its weight, it was absolutely nothing, felt like i was lifting my grandfather’s walking stick. I shot 10 shots not at balloons but at those small plastic animal silhouettes used to teach kids, & i was able to hit 9 times, i was surprised by the trigger weight so i missed my first shot. I gathered some onlookers as i was mentioning the target to my colleagues prior to every shot, & with every hit my smile widened, shoulder broadened, it was amazing.
I was really impressed with its accuracy & smooth shooting cycle. It felt almost with no recoil as if its a PCP & great smooth trigger with nominal trigger pull weight. The most amazing thing i have ever seen in my airgunning life is the way the gun was cocked. The shop owner was holding the barrel & the stock was towards my side, shop owner raised his wrist & the gun got cocked on its own weight.
I enquired about the gun from Basuda & found out that i misread the model no to be 28 instead of 23, its SDB 23. i ordered one from Eastern Arms Kolkata & received it within 7 days on 2nd February.
That weekend i was eager to get back home & have a look at that shorty. I found a comparative smaller box than that of ihp, well packed in a box. On opening the box i found that miniature air rifle & straight away fell in love with that. The stock is smooth with brown finish & good blueing. Fired few shots & my combro chronograph is reading it at 531 fps with 7.7 grain mastershot yellow box pellets, cocking was gritty requiring around 17kg of cocking effort, trigger was super heavy to whooping 7 kgs but the only thing good was its vibration less. So like all Indian springers it also demands tuning. As said before its a light weight miniature air rifle mainly for young shooters but if you want your wife to indulge in shooting its a good option because of its weight & less cocking effort & less intimidating. Total Length-940mm, Barrel Length-313mm, Receiver Length-235mm, Pull Length-330mm, Length of wooden stock-570mm, Overall Weight-1.92kg. Since the pull length of the stock is less its not going to be easy for people with longer limbs. I am 5’11” & i had to adjust myself to correctly align with the sights. The sights are not like conventional/full size air rifle, there is a metal strip adjustable for both windage & elevation. But the windage adjustment is adjusted by loosening the main screw & moving that strip left or right accordingly. Dont ridicule me but once adjusted it stays on place & the hits target every time, if i do my part correctly of course.
Here are the dimensions that i noted
Spring
Length-220mm, Coils-34 nos.,Pitch-4mm,Coil Width-2.57mm, Inner Dia-11.59 & 11.76mm, Outer Dia-16.37 & 16.37mm
Piston
Inner Dia-17.42mm, Outer Dia-21.18mm
Piston Rod Dia-7.9mm, Piston Rod Length 123.79mm
Rear Guide
Rear Guide dia-10.98mm
Rear Guide length-69.14mm
Rear Guide sleeve dia-20.92mm
Rear Guide sleeve width-5.48mm
Seal Dia-22.5mm
Receiver Dia-22.4mm
1st Tuning
I disassembled the gun with the help of my spring compressor, though there is very little preload on spring. I had to place a wooden block infront of the receiver as length of the receiver is small compared to conventional air rifles. I degreased all the parts & started polishing the piston latch rod, piston sear, piston wall (inside & out), spring, trigger sear first with 600 grit, then 2500 grit wet & dry sandpaper & finally with metal polish to give mirror finish. Upon dismantling i soaked the leather seal in vegetable oil overnight. Removed all burrs & foreign particles from polished surface & applied precihole moly in the piston rod, rear guide, spring, trigger interface, cocking linkage & reassembled the gun. Firing couple of pellets i could smell dieseling but didn’t see any smoke. Seniors with experience of using leather seal can give me their views. Now cocking effort has reduced with lesser grittiness while cocking the rifle, but i could feel some vibration when i pulled the trigger, since i didn’t increase the sear angle of the piston (only mirror finish) so i was not expecting a great deal of pull weight improvement. After firing around 200 shots i thought of giving it second round of tuning.
2nd Tuning
This time emphasis was given to polishing the piston shear for more manageable trigger pull weight. Firstly the sear angle was increased for lessening the trigger pull weight, this is a trial & error method & things can become dangerous if too much of metal is polished off from sear resulting in auto fire, hair trigger. Once while adjusting my ihp trigger pull weight i increased the angle so much that it was misfiring. The safest way to check misfire is keeping the barrel held tight by one hand after cocking & gently stroking the trigger with trigger finger to see if it releases at even mild jerking/vibration. Though its time consuming, laborious job but it has its merit & satisfaction. I bought dremel tool accessories to use it by attaching it to my drill machine & it works perfectly. These accessories include grinding, cutting, buffing, sanding, brushing tips which can be attached to a drill machine & works just like a dremel tool. Grinding stone was attached & placed at an angle to slowly to gain the desired sear angle. Then after getting that angle i usually first use 600 grit, then 2500 grit wet & dry sandpaper & at last metal polish, but in this case i only used 600 grit for smoothing out the interface.
Since after first tuning i felt vibration so i thought of shortening the mainspring. I cut off 4 coils making it now 30 coils with 195mm free length. Now for squaring the spring end, put the cut end on a gas stove & let it get red hot & then with a set of pliers flatten that end by pressing it. Then grind it using sand stone or dremel grind head & finally use 320/600 grit, then 2500 grit wet & dry sandpaper & at last metal polish it to give mirror finish. This time i used maccari tar on spring to dampen vibration & maccari moly in all contact points.
Upon assembly first thing i did was checking the trigger sensitivity/release as mentioned to avoid autofire. Then i cock & de-cock it few times to uniformly distribute the grease/lube. Now cocking effort is reduced to only 7kg with trigger pull weight to 2.2kg (didn’t mirror finished it yet) & that vibration i was talking about is all gone, with smooth firing cycle. Also added a rubber buttpad as there was none supplied so i paid a visit to nearby cobbler with impression of wood on a piece of paper & got back home with a nice rubber butt pad. Fixed it to the end of the stock with dendrite & left it overnight.
Mastershot flat head (yellow box) 7.7grns- 354(2.14), 371(2.37), 354(2.14), 370(2.35), 364(2.27), 370(2.35), 362(2.45)
JSB exact 8.44 grns- 423(3.34), 419(3.29), 431(3.47), 418(3.26), 429(3.34), 405(3.08)
At 3rd tuning I cut off 2 more coils & pressed 1 coil making free length to tried to replace the leather piston seal with weihrauch 25. Hw 25 seal has the same dia as that of SDB23 seal but seal is different compared to conventional seals. So after trying all the available resources of making an adaptor for HW 25 seal i gave up the idea. I polished the piston sear 600 grit then 1200 followed by 2500 grit wet & dry sandpaper & at last metal polish it to give mirror finish & achieved 900gms trigger pull weight.
Velocities achieved using
Mastershot flat head (yellow box) 7.7grns- 315(1.69), 318(1.73), 327(1.83), 329(1.89), 325(1.80)
JSB exact 8.44 grns- 371(2.56), 388(2.80), 375(2.62), 394(2.9), 377(2.64)
5 shot group standing at 7 yds
I am planning to go for 4th tuning where i will add a synthetic seal & if possible derlin top hat & rear guide for lowering piston weight.
Regards Moulindu
.I will get one from Eastern Arms & try it.
