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domer_pyle · Senior Member

If I were to upgrade for power would I need both a flat top valve AND piston? Or would the piston be enough by itself? And could anyone exlain what the upgraded valve does? Thanks in advance

rsterne · Moderator

The standard piston has a rubber cup that (loosely) matches the cone shape on the top of the valve.... A flat-topped piston is flat and must have a flat topped valve to meet up with.... or you will lose instead of gain.... Where you gain is in the rigidity of the F-T-P (metal sealed with an O-ring) and lack of headspace (because you set the piston up to just touch the valve, flat to flat)....

Bob

domer_pyle · Senior Member

Cool, I found some info about it but that was much more informative. With that combo and a 14" barrel would 700 fps be out of reach? Keep in mind I dont want to pump much more than 10 times per shot

rsterne · Moderator

If you are talking .177 cal you should be around 600-625 with a 14" barrel at 10 pumps.... I got ~550 with the stock 10" barrel and ~700 with a 24" barrel.... both at 10 pumps with F-T-P....

With a stock hammer spring my gun started retaining air at 16 pumps.... At 15 pumps I got ~620 (10") and ~830 (24").... You could probably get close to 700 fps @15 pumps with a 14" barrel.... You can get more with a Disco hammer spring but you will have to pump more than 15 pumps as well....

Bob

domer_pyle · Senior Member

Thanks guys, that about clears up everything I needed to know. I was hoping to be able to fit this in a backpack to maybe bag some squirrels while camping aside from plinking but it looks like I'll need that 24" to keep a more ethical velocity. Ah well, no shoulder stock for me! That's fine as well since I'd like to keep it a pistol and not a cross dresser

rsterne · Moderator

Alternately, you could use a 14" .22 cal barrel and end up with the performance of a 2289.... You will get ~500 fps in 10 pumps.... and up to ~550 with a bit of valve & port work.... At 16 pumps, you should get 600-640 fps depending on porting....

As a comparison, 500 fps with 14.3 gr. pellets (.22) is about 8 FPE.... It takes 675 fps with 7.9 gr. pellets (.177) to get the same killing power.... I prefer the .22 hands down for hunting.... plus the 13XX / 2289 platform is more efficient in .22 cal so you get more FPE per pump....

Bob

domer_pyle · Senior Member

I see. How hard was it to swap out pumpers/compression chambers on yours? I think I may have to stay .177 though as that's my preferred target caliber. Thanks a lot for your replies, you said more with less than everything else I could find anywhere