10.7 FPE Air Rifle SN-45
Posted: Mon Sep 08, 2014 3:54 pm
http://indiansforguns.com/viewtopic.php?f=2&t=22389
This is in continuation to my earlier post wherein I had given the out of the box observations on my new breed gun ,SN-45.
This gun is SDB45 Classic except its barrel and back sight are from IHP and so requires serious tuning.
The tuning process:
Disassembled the gun first.
The main spring is of 40 coils and blinded by rage due to its hard cocking, punished the spring by kept it in cocked position first for 12 hours then again for 6 hours with a gap of 6 hours.
Removed two coils and kept the free length at 28.7 cms with 38 coils. Both ends were grinded and finally smoothened on sand papers. The gap between the coils measured to be 5 mms.
The piston was completely dark with all dust and rust which was polished by 320 grits sand paper both inside and outside to give a gentle look.
It has oil-tempered sear rod which helped me to give mirror finish with 92-93 degree taper.(Caution : please do not try this unless you are quite at home with this job.)
The depth of the sear is 3 mm, which I wanted to reduce to 2.5mm yet it could not be done due to hardness of material.
The interface of the trigger is given super mirror finish with same 320 grits.
A Coke bottle part used as sleeve inside the piston wall to stop buzz of the main spring.
A thrust washer is put through sear rod to offer a nice surface to spring to get easy torque.
Polished the inside of receiver with handmade honing tool with 400 grits sand paper.
Fitted last TTI commercial seal on piston, softening by putting it in hot water.
Cleaned every part in kerosene oil.
I was desperately in need for moly but did not have a pinch of that at all.
One IFGian Kaushik had given me local moly, certainly no where close to 60% Mos2, but good enough for ARs, were used sparingly on spring and piston rear bearing.
A specially made spring guide is used with OD of 13.5 mm to match the main spring ID.
A thin layer of this moly is also given on the guide.
The cocking shoe is filed to remove uneven surface.
TTI seal received a little nick on lip while putting in receiver. The seal then resized and put back again.
It was little tight fit inside the receiver.
It is noticed that with synthetic seal the piston stroke increased to 8 cms and so swept volume went to 49 CC.
The breech seal is replaced with Welding hose and kept 0.5 mm protruded.
I was longing for Precihole used seal but that was not available at that moment.
The advantage with used seal is that, it starts giving maximum FPS from very first shot unless too misfit.
The entire assembling was done and now it was ready for testing.
Velocity:
Unitedshot 6.8 grain---------------- Max 840 FPS with pellet pusher , no increase.
Gsmith amateur 8.2 grain-----------Max 739 FPS. With pellet pusher 772 FPS.
Mastershot Flat Head 7.7 grains—Max 740 FPS with pellet pusher 775 FPS
840 FPS was really palpable at 40 yds, taking out dust from wall every time.
All above datas of Chonoconnect.
Noise:
74 dcbls at 5 mts from muzzle, not noisy.
Vibration:
4.2-4.3 Richters with all pellets. Quite good for accuracy
Accuracy:
Not very good, trigger is not that smooth as of now. It is not engaging at the same place every time.
Cocking Effort :
Less than earlier pull, manageable.
Over all feel:
Much smoother yet the need for quality moly is felt.Easy to shoot. The seal yet to get set.
Conclusions:
The gun is still breaking-in. I suspect that it has capacity to deliver a little better FPS due to long stroke.
The piston weight is in the range of 260-270 gms, due to which it gives low recoil.
The improvement in accuracy is on the card once it passes 1500 shots.
I have to wait till then…………
Basu
I request SathyaSniper to post some photos on my behalf and oblige.
This is in continuation to my earlier post wherein I had given the out of the box observations on my new breed gun ,SN-45.
This gun is SDB45 Classic except its barrel and back sight are from IHP and so requires serious tuning.
The tuning process:
Disassembled the gun first.
The main spring is of 40 coils and blinded by rage due to its hard cocking, punished the spring by kept it in cocked position first for 12 hours then again for 6 hours with a gap of 6 hours.
Removed two coils and kept the free length at 28.7 cms with 38 coils. Both ends were grinded and finally smoothened on sand papers. The gap between the coils measured to be 5 mms.
The piston was completely dark with all dust and rust which was polished by 320 grits sand paper both inside and outside to give a gentle look.
It has oil-tempered sear rod which helped me to give mirror finish with 92-93 degree taper.(Caution : please do not try this unless you are quite at home with this job.)
The depth of the sear is 3 mm, which I wanted to reduce to 2.5mm yet it could not be done due to hardness of material.
The interface of the trigger is given super mirror finish with same 320 grits.
A Coke bottle part used as sleeve inside the piston wall to stop buzz of the main spring.
A thrust washer is put through sear rod to offer a nice surface to spring to get easy torque.
Polished the inside of receiver with handmade honing tool with 400 grits sand paper.
Fitted last TTI commercial seal on piston, softening by putting it in hot water.
Cleaned every part in kerosene oil.
I was desperately in need for moly but did not have a pinch of that at all.
One IFGian Kaushik had given me local moly, certainly no where close to 60% Mos2, but good enough for ARs, were used sparingly on spring and piston rear bearing.
A specially made spring guide is used with OD of 13.5 mm to match the main spring ID.
A thin layer of this moly is also given on the guide.
The cocking shoe is filed to remove uneven surface.
TTI seal received a little nick on lip while putting in receiver. The seal then resized and put back again.
It was little tight fit inside the receiver.
It is noticed that with synthetic seal the piston stroke increased to 8 cms and so swept volume went to 49 CC.
The breech seal is replaced with Welding hose and kept 0.5 mm protruded.
I was longing for Precihole used seal but that was not available at that moment.
The advantage with used seal is that, it starts giving maximum FPS from very first shot unless too misfit.
The entire assembling was done and now it was ready for testing.
Velocity:
Unitedshot 6.8 grain---------------- Max 840 FPS with pellet pusher , no increase.
Gsmith amateur 8.2 grain-----------Max 739 FPS. With pellet pusher 772 FPS.
Mastershot Flat Head 7.7 grains—Max 740 FPS with pellet pusher 775 FPS
840 FPS was really palpable at 40 yds, taking out dust from wall every time.
All above datas of Chonoconnect.
Noise:
74 dcbls at 5 mts from muzzle, not noisy.
Vibration:
4.2-4.3 Richters with all pellets. Quite good for accuracy
Accuracy:
Not very good, trigger is not that smooth as of now. It is not engaging at the same place every time.
Cocking Effort :
Less than earlier pull, manageable.
Over all feel:
Much smoother yet the need for quality moly is felt.Easy to shoot. The seal yet to get set.
Conclusions:
The gun is still breaking-in. I suspect that it has capacity to deliver a little better FPS due to long stroke.
The piston weight is in the range of 260-270 gms, due to which it gives low recoil.
The improvement in accuracy is on the card once it passes 1500 shots.
I have to wait till then…………
Basu
I request SathyaSniper to post some photos on my behalf and oblige.
