Flat Top Piston?

[.22 Varmint]

   I have a custom Crosman 1322 and I am thinking of adding a flat top piston and valve to add on a couple of foot pounds for hunting. Do flat top setups have any downsides or any special maintenance? What kind of energy figures should be expected with a 10.25 inch barrel using .22 JSB 18.1 grains? Is the flat top upgrade worth it overall? Thanks for any advice.

Andrew

[rsterne]

The flat-topped piston reduces the number of pumps it takes to get to a given pressure.... With the stock setup, it is difficult to get to the point where the valve retains air, but with the F-T-P it's easy.... A stock valve and hammer spring will retain air at around 15 pumps, which is around 600 fps (14.3 gr.) with a 14" Barrel (a 10" will be less).... If you take the sear spring and put it inside the valve (and put in a lighter trigger spring) you will get to about 18 pumps and about 650 fps (14" bbl) before the valve retains air.... To get more power than that, you will need a heavier hammer spring from a Discovery.... or a Rear Velocity Adjuster (RVA - hammer spring tensioner).... or both.... With a Disco spring and a LOT more pumping (30ish?) you can get to about 750 fps (14" bbl).... I'm guessing you can knock about 50 fps off those numbers with a 10" barrel, but it's just a guess....

Bob

[Rescue35]

http://www.gatewaytoairguns.org/GTA/index.php/topic,11908.0.html

Link to where I ran the PC77 .22 with flat top piston over the crony and compared it to a stock one. I'm happy to hunt with this gun. It is getting 12.4 FPE

[.22 Varmint]

Thanks guys for the input. If I install a Flat Top setup, I will keep you posted on the results. Thanks again.

Andrew

[MartinDWhite]

The difference between barrel length is about 10 fps per inch of barrel. This is an often quoted number that I have verified with my own testing. So a 14" barrel will be about 40 fps faster than a 10" barrel with the everything else the same.