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If you ar concerned about the stroke, purchase a Benji HB pistol inlet valve. It is shorter in length AND has much less volume. You would see gains immediatley on 10 pumps. However, you will then need to add some length to the factory piston (slightly less than 1/2"). To do this, (1) you can cut the piston rod then thread both ends (1/4x20 threads) or, (2) heat up the end where the lever link attaches and pull out the piston rod and thread the hole to 1/4x20 thread and the piston rod. You then would need to use a sleeve nut to capture both ends.
As far as the slot. The slot should have needed to be extended the same amount that has been removed from the tube, (edit) that's if you were using factory components. I did not scroll far enough to see the piston unitl later - oops. Put a rod in that piston (make it longer), problem/stroke will be solved.
Survival Benji? Now time to bed liner the stock.
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if your a good shot, probably no difference
bigger game might be taken easier with bigger pellets, smaller pels means you can carry more pellets
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With the greatly reduced stroke length you've gone with, you'll probably be disappointed with the power that will result if you convert the gun to SSP. Since your pump now moves less than half as much air per stroke than stock, you'd probably find it will also produce less than half as much power as Phil's if redone as an SSP. Maybe much less.i cut the new slot and drilled holes for the tube plug. I didn't realize i would need to cut the slot so long to accomodate the original pump arm. i ended up losing alot of stroke volume. i think i'll have to just make a new valve using phil's idea and turn it into a SSP. as it is now with the reduced volume in the valve and about 3 inches (approximately) of air per stroke, it shoots a 14.3g cphp at 530 fps on ten pumps...
im still waiting on the guy at the machine shop to finish the 7/16th sleeve that will fit over the end of the barrel
here's some pics of it:
the bottom gun is my 397 for comparison