FAS 6004 Project

[WyoMan]

Hi Steve, I think I follow what you did but a picture would really help (if that's possible). Sounds like it worked really well though.

Here's a very brief summary of the effects of altitude on SSPs...


What's noteworthy is that the muzzle energy doesn't drop off as fast as the atmospheric pressure... maybe there's better pump stroke efficiency at lower pressure... or just not enough data.
I'm thinking that a perimeter seal on the face, like a very shallow pump cup - that traps all compressed air to the center (direct flow thru the port), might be the ticket...

Wyo

[clarky]

Interesting buddy, i have never seen a table with atmospheric effects like that...

I am unable to be certain if this new piston face seal is simply shoring up the regular seal on the diameter, for better sealing off the transfer port after air has been compressed, or if it has created a mini high compression resevoir (my best guess) but it added a big gain...
Finale pellets went from 330 fps (*(&^ this thing is low stock) to 380 fps....
Its about the best result ive had from the various mods ive performed similar to yours.

Incidently, returning to the piston stock....but with the groove cut for the O ring ( i.e with no O ring) saw the velocity hit an all time low of 290 fps....
Proving conclusively that peoples ideas to go in the opposite direction by creating more volume is going in the wrong direction......this thing needs less volume for more compression thats for sure...

Have you tried removing some material off the valve plunger....its got a lot of excess angle on it after the tiny O ring which must be restricting flow...

[WyoMan]

I believe that's correct, Steve.. that increasing the valve (or headspace) volume is the wrong way to go. One of the first things I noticed was the really easy pump effort - indicating that it could use a little more compression.

I see what you mean about the valve poppet. It extends (to what looks to be) further than necessary beyond the o-ring gland. I think the main restriction to flow would still be around the o-ring. But I don't know. I am, however, always leery about opening things up (to improve flow) when there's so little flow to begin with. It may help but it will create more transfer volume to fill. I wonder about all the guns with long transfer ports (riser breeches for shrouds, mags, etc) - does that reduce muzzle energy / efficiency....maybe not?

Wyo

[JCBinWV]

Gary- reviving this older thread of yours as I have a couple questions on something you mentioned in your first post...  "Cleaned the piston, felt wick, cylinder and flushed the valve."

I've just about had enough of whatever that lube is FAS/Chiappa used in the assembly of the piston!  I'll probably be tearing mine apart for a good cleaning soon.  You said you "flushed the valve" - how did you do this?  Did you dissect the valve, or just run a cleaner/degreaser through the transfer port?   Seems like I've read somewhere that getting the valve out is difficult at best & I'd rather not get into that...

Also, what did use to clean the felt wick?  Wasn't sure if a degreeser would cause it any harm?  May use hot soapy water (w/ Dawn) instead.

Thanks in advance!
jc

[WyoMan]

JC, I didn't remove the valve... I sprayed WD-40 into the cylinder (with the valve open) until the WD-40 came out the transfer port. Then blew it out with air. I did that about three times and then blew air thru the transfer port with a rubber-tipped nozzle.

The felt wick was soaked in WD-40 and then squeezed to remove the contaminants (for lack of a better term). It was a rinse, lather, and repeat operation until it was clean. BTW, WD-40 is a pretty good degreaser. thanks -

Wyo

[JCBinWV]

JC, I didn't remove the valve... I sprayed WD-40 into the cylinder (with the valve open) until the WD-40 came out the transfer port. Then blew it out with air. I did that about three times and then blew air thru the transfer port with a rubber-tipped nozzle.

The felt wick was soaked in WD-40 and then squeezed to remove the contaminants (for lack of a better term). It was a rinse, lather, and repeat operation until it was clean. BTW, WD-40 is a pretty good degreaser. thanks -

Wyo

Gary -
I was hoping you were going to say you didn't dissect the valve.   WD-40 ... good stuff, just don't confuse it for a long lasting lubricant, right?   

Thanks for the feedback.

jc

[WyoMan]

Right you are, JC. I use 20wt ND for the piston o-ring.. applied thru the intake hole when the felt wick is aligned. I've tried 30wt ND but it doesn't wick thru the hole very well. The lighter weight (20) isn't quite as "tacky" but that isn't necessary when the wick is saturated.

Link to what the cleaned wick looks like:
https://www.gatewaytoairguns.org/GTA/index.php?PHPSESSID=e954948fe94de2ab9cf24294ace04a00&topic=135691.0

Thanks-
Wyo

[clarky]

You ever thought about a 2 pump concept for this gun buddy ..

[WyoMan]

You ever thought about a 2 pump concept for this gun buddy ..

Do you mean a two-stage pump like the Alecto... or a check valve like a regular MSP?
I suppose a check valve assembly could be machined into the valve body... as a complete unit that went in like a threaded insert... drilled and tapped in line with the inlet port....?
Sounds a little like a self-destruct mechanism 

Wyo