PGP velocity drop off

[Drcemento]

Been Building out my "PGP that I would actually want to play with" - I desoldered it, drilled out the transfer port, and managed to get 3 really nice wedgits in it so two big hurdles on my list solved. Put it all back together and ran some paint through it. first shot is low velocity, second through 5th are 280 then It drops to a steady 220 for about 15 more shots.
component valve, full rebuild with Junkies kit and 12 g seal, has a junkies RVA. I tried a lighter but slightly longer valve spring I had laying around and same story. RVA cranked pretty far in.
A couple 12grams looked barely pierced - another 2 had distinct but small - 1/32 holes

read the threads about de-volumizing..... do need to go down that road? new seal to thick and not enough pierce? valve pin and cup seal fine. no leaks. any ideas?

[Trbo323]

Too much volume after the valve was my first thought, if you have an easy way to test that I would go there first

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[Drcemento]

after the valve - as in I opened up the transfer port to much? i went with 9/32 instead of 5/16

[Trbo323]

Maybe, the more I'm thinking about it though I would probably go after that pierce pin first. Get it to open up the 12g more

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[Socalpumpballer]

Pgp junkies 12 gram seal is a little thicker and harder than a standard seal. Even if you get the 12 gram to pierce it might be too shallow for good air flow. Try tightening the 12 gram screw a little more before piercing. Obviously it’s easier with a fast change knob. Also using a slightly longer main spring especially if you upgraded to a RVA. I wouldn’t go lighter on the valve spring. A longer valve spring will choke the valve that’s probably why you didn’t see improvement with the lighter/ longer spring

[Myfeetupontheground]

I would like to discuss this further. I haven’t had any reports of issues with the thickness of the face seal, but I am certainly open to making it better!

Pgp junkies 12 gram seal is a little thicker and harder than a standard seal. Even if you get the 12 gram to pierce it might be too shallow for good air flow. Try tightening the 12 gram screw a little more before piercing. Obviously it’s easier with a fast change knob. Also using a slightly longer main spring especially if you upgraded to a RVA. I wouldn’t go lighter on the valve spring. A longer valve spring will choke the valve that’s probably why you didn’t see improvement with the lighter/ longer spring

[Socalpumpballer]

Honestly keep them the way they are. Shoot to pierce Sheridans are just finicky

[Drcemento]

Update:
My PGP junkies order came in - spring kit and docs changer amongst them. after a bunch of changing around springs and trying things out to no avail - I was still getting pretty bad drop off and what looked like not very good piercings of the C02 and lots of leaking noises after pumping or firing with the lighter valve spring, I Decided to see if I could shave off some of the face seal - this turned out to not be super hard with a new single edge razor and some patience.

TEST 1 I fired it up with the junkies longer main spring, rva and stock valve spring - essentially, same story - shot 1 has always been a dud to get the co2 pierced. 1-4or 5 might be good at 280 or so, then dropping to 220 with no recovery, i will confess I was not chrono'ing each shot like in the next test but - the piercing of the C02 was far far better than anything I've seen yet

TEST 2 junkies longer main, RVA with maybe 1/2 turn on it after it started engaging spring and this time I swapped out the valve spring for the junkies spring. shots as follows:
shots were always 10 -30 seconds apart except some of the dry fires which i did quickly.
Keep in mind barrel iD was 687 by my calipers, and I pounded wedgits in, so not rollouts at all.
1 - dud
2- 250 - +2 turns on RVA after shot
3- 257 - + 1 turn
4- 274
5- 283
6- 281 - 1/2 turn
7- 263 + 1/4 turn
8-250
9-257
10-248
11-252 + 1 turn
12, 13, 14 dry fired
15 - 267
16-19 dry
20- 216
21 237 - had waited 5 minutes to fire after shot 20

These were the best results yet. at this point I would say the thinner face seal and lighter valve spring/ longer main really helped. but what now? - I realize its C02, and not Ideal, but I want to take this as far as I can and get a more playable gun. I'd settle for 15 shots in the 270-280 range.

have i not opened the transfer port up enough? - i drilled out and put a 1/4" ID brass tube in there. I know that Walz liked 5/16

de-volumizing the chamber that the valve spring is in? - I think I could 3D print a sleave to narrow it up

plugging 3 of the 4 holes in the valve itself - a tap and brass screws could do that, but would I need to then register the one port verticaly like a cocker?

[Drcemento]

OK - way to much time on this and way to many wasted 12grams, But I got consistent results pointing me in the right direction!

I dug around the junk box and found a component valve assembly to hack on.

I started by Plugging 3 of the four valve holes and printed a sleeve to take up space in the chamber with the valve spring this was a total dead end. maybe 20 fps.

Next I pulled out the sleeve in the chamber. this instantly gave me better results but still very low velocity, so I decided what the hell - bigger might be better, so I drilled out the one remaining valve hole to 7/32 and put it all back together - Bingo! - this got me 13 shots in the 260 range - no matter what I did with the RVA

going with the "Bigger is Better" theme I decided to go for broke drill the valve hole out to 17/64 and then go in ream out the horizontal chamber a little with a 15/64 bit. this matched the larger transfer port I put in
Re- assembled and got the following:
again RVA set 1 turn in from starting to engage the spring. longer junkies spring, lighter junkies valve spring, shaved down face seal.

1 - dud
2- X
3- 296
4- 304 - backed out RVA 2 turns
5- 283
6- X
7- 276
8-293
9-283
10-277
11-283
12-276
13-272
14-267
15 - 272
16-274
20- 265
21-265
22-253
23-241
24-X
25-218

super happy with these! with Walz's 5/16 transfer port in mind I may try to push this even further, but I've never shot a PGP that held those numbers. took lots of photos and will try to compile what I did better. maybe I'm just re-inventing the wheel, though I have not seen much about valve mods. its totally doable with basic tools and I could not believe the results

[Cal440]

Congrats on your results, look forward to your photos. Will use your findings when I work on my Sheridan. Thanks for posting.

[Myfeetupontheground]

(PGPJunkies here) Do you have an extra face seal? I would like to know what results you would get with the standard (unshaved) faceseal, now that you have done all the other mods. The face seal thickness was based on the original thickness. But I am certainly open to modifying them. I had one PGP that had trouble with the initial pierce, but when I measured the pierce pin assembly, it turned out to be much shorter that the usual pierce pin assembly. Anyways, thank you for all the data. If you dont mind posting the data, I will send you another face seal for free.

[Drcemento]

Yes, I definitely want to backtrack and put the OG springs back in and see what happens. I have extra of the junkies seals so I’ll swap that back out and see if the valve mods negated the need for a thinner face seal. I have another un-touched PGP valve and want to see if there is a difference in pierce pin lengths.

[Drcemento]

Myfeetupontheground ok I had some time after grocery shopping and soccer games to swap out the cut down face seal for a new off the shelf junkies face seal. I'm happy to report it appears to not be the culprit in performance. I got 20 shots consistent with my best numbers above. I kept the lighter junkies valve spring and longer main spring in.

It should be noted that it really barely pierces it compared to a shaved down one. my pierce pin measures 0.73 as shown below

it should also be noted that time between shots matters - allot. waiting a minute or two will often get the shot back up to 290 (this is regardless of face seal)

I would think that a slightly thinner face seal in the future would not hurt anything and possibly offer a better more consistent pierce, especially with the OG C02 cap.

[Myfeetupontheground]

Thank you for the update! I really appreciate the data! I am planning to do some testing as well. And I am already looking into where I could source a thinner material to process.