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BAM 51 ramble (att. Darryl)

June 23 2012 at 9:39 AM
robert  (Login gubb33ps)
YF

Want to thank Ed for his suggestion, reducing the sear spring did reduce drag on my striker enough to make a difference in shot count. Understand, not talking about the pull weight...didn't change the other springs that control that.

Darryl:

Think you can get to 28X30 (28 foot pounds/30 shots) or at least very close to it. I tend to use 3% of max. speed to set the sweet spot, so if you the peak shot was 950fps (lets say 18gr.), then the velocity variation limit would be 28fps (950X.03 = 28.5).

(Percentages make it tougher on low powered guns...a 600fps gun would have to live inside of 18fps while a 1000fps gun would have 30fps to play in).

Do get tired of taking the gun apart...so don't. Tuning for power and shot count, will worry about accuracy later, so I don't put the gun fully together for testing. Don't bother to mount the scope, the barrel band, or the brake (even putting it in the stock is optional). Need a bit more time setting up a firing cradle to get your chrony readings, but saves time/effort in the long run.

The Book may not have been about the .22 versions, but the directions of change the mods do apply. You may not be able to do X and Y and come out with exactly Z, but you will get the same direction of change.

Afraid I got side tracked at 25 foot pounds (which is more like 28 foot pounds with 21gr. Pellets). And I still only want to run it at 150BAR.

This looks good for short range (tested at 22 yards), but you have to be critical when using short range. The real variation in these 40 shots is about 50 fps. That's OK for 20-30 yard shooting, but really would be better to say inside of half that for longer distances.
[IMG][linked image][/IMG]

Cut up and put together like this, with group centers marked and joined, the 40 shots start to look more like a shot graph. More like 25 good shots than 40. If trying for some 75 yard groups, would probably try to stay in the spot where the best 15 shots live (targets #4,5,6)..
[IMG][linked image][/IMG]

HINTS that it may benefit from a new(smaller diameter) valve seal:

The difference in energy between light and heavy pellets is kind of high, Points to a lot of air being moved per shot.

They tend to valve lock with just a small over fill. Valve closing force is the air pressure acting on the area of the valve seal (along with valve seal material and shape). Air pressure is the same as for other PCPS, takes more of a hit to open them up at the shot, so the valve seal area is probably larger.

Problem spots ( first one related to the above):

Skinny valve stem seal...large valve seal area...heavy closing force...strong opening hit. Seems this is why they occasionally just drive the valve stem right though the valve stem seal.

The screw on the left side of the bolt (the one that actually pulls the striker back) works loose. If you let it get wobbly-loose will bugger up the threads.




    
This message has been edited by gubb33ps on Jun 23, 2012 10:45 AM
This message has been edited by gubb33ps on Jun 23, 2012 10:21 AM
This message has been edited by gubb33ps on Jun 23, 2012 9:47 AM
This message has been edited by gubb33ps on Jun 23, 2012 9:45 AM


 
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