New 392 clone build

[DanD]

I like the idea of getting the most out of the least, especially on a pumper.
Whenever I mod a valve I usually stuff it a little instead of increasing the capacity.

Yes, high efficiency  is what is significant about this gun. Makes the “air conserving pumper” concept obsolete.  625@4 easy pumps every time. No guesswork.

I used to have a debounced C9. It had a hammer spring preload adjuster so you could fine tune the hammer strike to dump just the right amount of air to stay consistent . Iirc, mine took 6 pumps to precharge, then 3 pumps between shots all day long for 610 fps with .20 cal 14 .3s.
I've been imagining a debounced gun like yours doing 800 on 4 pumps.  But maybe there's not any room in the valve to hold air between shots due to such high efficiency.

[Psipumper]

Any plans to flat top the valve/piston?
Fairly easy and will yield good gain.

Flat top won’t help here because I have already reduced the the headspace to a very small amount. Regardless of the shape , zero air volume is zero. There are pros and cons to the flat top. Although it can be done, an  adjustable piston is already available from Mac1. The factory cup seals well with replacements available.  If you remove the cone shape and extend the flat top piston to meet it, the air hole at the top of stroke would not line up.
The one way a flat top piston would be better: A high volume valve that uses a spacer between the valve halves . This would return the position of the flattened end of the valve to use the air hole. Maybe.
Probably easier ways to gain more valve  volume  in the 392PA though.

[Psipumper]

Nice numbers. What do you have planned next?

I am going to return to adding the delrin exhaust valve . Getting a good seal on delrin  can be troublesome on a pumper. Maybe more trouble than it’s worth? If it doesn’t add 20 fps ,it’s too much trouble.
Then on to the final stretch to wrap up the clone project .
Revisit my original gun to add things learned from the clone.
Possibly start a new thread on the late model trigger .
I am asking around locally looking for a 392P or a 342 . I really don’t need one but I think I should repair one to have a look around.
Who knows, I may stumble onto a 50 yard tack driver.

[Tack Driver 10]

The best way to FT a 392 valve that I've found is to trim the front part of the valve 1/2".
Make a new FT valve cap that is 1/2" long so the original valve length is maintained.
This would make the valve a 3 piece.
The check valve is machined to .030" to the front of the FT minimizing dead air space.
Duro 90 poly O-ring seals on the valve and piston.

The FT eliminates the cone resulting in a gain in stroke plus minimizes dead air space.
Volume is variable using spacers depending on desired result.
Never had a problem getting delrin valve stems to seal.

Here are some examples from other guns. The principles are the same.

[Psipumper]

I agree that a flat top piston is possible. Just a little too late to change course on this one. I will keep that in mind if I decide to build a max power altered gun.

[Longbow]

WOW ! This is a great post.... I had a lot of trouble getting the delrin to seal properly as well.... I needed to increase the spring pressure. I modified the original valve stem by removing the crappy Rubber seal that is destined to fail and replaced it with a piece of the delrin popet/ exhaust seal.... it's much more efficient at dumping all the air out. The Rubber seal is too soft and closes up too quickly leaving air in the valve...... in the picture you can see the new delrin seal installed and the old damaged seal sitting on the side with brass shrapnel all over it....

I hope you continue with this post , it's been very informative and entertaining.. also could you please make me one of those Wicked awesome barrel breaks ! 

[RCO]

Charles, Did you ever get the Delrin to seal? What did you do to change the hammer?

Rob

[Psipumper]

Charles, Did you ever get the Delrin to seal? What did you do to change the hammer?

I didn’t have any trouble with the delrin sealing after sleeving the valve stem hole to correct excessive clearance. I changed the stem diameter to 3/32 .  Unfortunately, the change slowed the gun 16 fps to 782.
After trying a few things without success, I made a new larger diameter exhaust and regained lost speed to average 805@8 pumps. 647@4 pumps.