Crosman 1300KT pressure ?

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fishinwrench

fishinwrench

Member
Nov 25, 2017
589
16
mo
Has a modified valve and piston but I cannot get a pressure increase after 14 pumps. You can pump it all day after 12 pumps and it never gets any harder to pump, and there's no FPS increase. It peaks out at 520fps whether you pump it 16 times.....or 25 times.

I don't think the valve is leaking because it will hold the pressure from 12-14 pumps all day long.

Why the hell won't it build up more pressure than that. I just wanna get this gun up to 12 FPE and I know they are capable of that....or SHOULD be.

Shouldn't each pump get progressively harder as pressure builds? Currently my 16th pump is no harder than my 8th pump, and I can't figure out where my air pressure is being lost at. Any ideas? Thanks
 
This goes back to the topic of headspace we discussed in your previous thread. Topping out at 12 pumps is in the ballpark of what I've seen with other Crosman pumpers in OEM form. Are the aftermarket go-faster parts adjusted to eliminate headspace to the extent possible?

Regarding the 12fpe goal, what is the caliber and barrel length?
 
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Okay yeah the 12fpe goal is reasonable with a 14in barrel in .22 cal assuming the headspace is adjusted out. The best way I know to tell is to remove the guts from the valve (so it won't build pressure). Then close the pump arm and you want to feel the pump cup bump into the valve face when the arm still has about 1/2" from closing fully.

I know it's a pain to have to do that but the problem with trying to do it with a fully assembled valve is that the pressure makes it difficult to distinguish when the cup reaches the valve, and any air that's trapped in the headspace will provide a camover effect that helps to keep the pump arm latched.

It won't be the fault of the pump cup itself being unable to build pressure unless it's damaged in some way. It's plenty good to keep building pressure out past 25 pumps.
 
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