1322 FLAT PISTON TOP THE EASY WAY

[bil601]

After turning the valve top flat I started to make a piston.  I got the Oring slot turned & was going to drill the hole for thre ajusting screw. Started going over the length  in my head so I measured the original piston & realized I could just turn a piece of rubber to fit the original shaft. Then I thought it would be nice to just fill in the cup to make it flat. So I ruffed up the cup with 100 grit warmed it with a heat gun & filled it with hot glue. It bonded great put it in the freezer for a while then finished the end on the lathe. No measuring, no ajusting, no special parts. 15 pumps with 22 cal. CPs was giving 500fps. Now 15 pumps 536fps.  No mods to the valve eccept polishing. I have been shooting it for a week now with out any problems. Ill have to see if it separates at some point, but for now Im likin it.

i like your idea as i have been looking to switch to a flattop setup.
my stock 1322 gives 525 fps with ten pumps using beeman h&n match.

here's a good valve mod

[bil601]

OK I heard you the first time LOL

[bil601]

Disregaurd my last post I was talking to someone else

i'm not tryin to give a hard time.
with you new flattop set up you should be moving more air per pump so now you need more room in your valve.

ok no problem

[bil601]

Yea I have done that to my gas guns. I am going to try smaller instead of larger. Im thinking high pressure & low volume. There seems to be a lot of extra air out the muzzel when I fire. Havent heard of anyone going smallerso Ill give it a shot.

a stronger hammer spring or a weaker valve spring will keep the valve open to use all the air.
you will just need to cock the gun before pumping.

[bil601]

Ive been trying to carry on two conversations at once been responding to myself. Yea I always cock it before pumping & there is no air left after the shot if I cock & fire again. The last three pumps are much harder now I am wondering if the plastic piston shaft isnt flexing. Also what grain are your pellets. My gun shoots Daisy wadcutters much faster than the CPs.

the H&N's are 13.75.
you can ease your pumping strokes by opening up the air entrance on the front of the piston with a drill bit.

if you think the piston shaft is flexing then use some epoxy to reinforce it.

[DanoInTx]

....a big advantage that the aftermarket pistons have over modding the original isn't just because they get rid of headroom between the valve and the piston, a bigger advantage imho is the fact that they don't flex at higher pressure.  The way you are doing the mod now you may get "some" advantage, but you wont really see much beyond 20-30fps until you make a rock solid piston.  The adjustable part is to adjust for optimal/minimal headspace between the valve and piston, there is very little advantage to that if the piston flexes and increases headroom again.  Solid delrin with an adjuster and double o-rings with a flat top valve to match will allow for much better performance, just making the piston flat on top doesn't really do anything.  Once you get it setup right you will be able to use a valve with more volume, but you'll also need a long barrel to take advantage of that volume/pressure, the 10" 1322/77 barrel wont do it.

Fun little guns to mess with, there are a ton of mods out there to try....enjoy!!!

[RCnMo]

heck, if you have a lathe, making the adjustable piston is a breeze. It's worth it too.

[bil601]

OK Im back what did I miss looks like lots of stuff. My goal is to get as much out of a stock barrel as I can I all ready have a rifle so I see no point in making another one. What I am after is as much pressure as I can put in the valve on no more than 15 pumps or less & getting it out of the valve as fast & smoothly as possible. So far I have opened the end of the valve on the piston end. I am going to open the transfer port to 1/4 inch. I am also playing with the end of the bolt. I noticed with the stock short probe I lost fps when I seated the pellet past the transfer port. Just seating it with the stock bolt gave me almost 18 fps more. Im sure it would hit 600fps with light pellets the way it is now.