Valve mod - pcp pistol - Kiwi Airgunners Forum

Very cool Paul, you are a talented engineer!

Looking good, cant wait to see it when its all finished.

Walk quietly, but carry a big stick.

Hi y'all, I got the lawns done tonight then went into the garage to do a bit more work on the pistol.

I had been struggling trying to find a leak. At first I thought it was a line on the inside of the tube from production, so I honed it with 300 grit on a dowel in the lathe. It wasn't this, so I took a serious look at my O ring grooves and I had left a small ridge on the sealing side of it. removing this seems to have done the job.

I reassembled the pistol and fired a shot over the chrony, and very interestingly it only read about 4 fpe. I figured this was due to it being too close because the next shot, from further away was better than I expected at a healthy 19.77 fpe. I still have to make the lockup device for the bolt/probe, so I am holding the probe in to fire. On the next shot I got 20.98 fpe.

I have learnt that making sure there are no leaks in the transfer port area has a big impact on the power output and you can loose a lot of energy through leaks.

I had cut a tapered lead into the barrel and I need to get a slightly thicker probe O ring too as it gets blown out of it's groove, so once I get that and the lock up sorted I am likely to see over 20 fpe for this .25 cal puppy.

I don't know how accurate it will be, but I am very happy with the results so far. 26.23 grn pellet @ 600 fps

It’s looking great! Healthy power too

J S Airguns
Air Arms TX200('s)
Theoben Sirocco
HW77
FWB 300s
Webley Patriot
One or two others...

Current projects:
Too many..

The main thing with drilling stainless is high feed and lower speed.

It is not the heat that hardens stainless. Regular 304 and 316 are non heat-hardenable.

They only become softer with heat. But they work-harden very readily (316 moreso).

So applying too little pressure to the drill causes it to skim along the surface

without starting a chip. This work-hardens the surface you're trying to drill.

The problem with heat is that it blunts the cutting edge of the drill

which leads to work-hardening of the stainless, accelerating the issue.

HSS with cobalt can handle higher temperature.

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J-S Members Profile Send Private Message Find Members Posts Visit Members Homepage Add to Buddy List Senior Member Joined: 20 Oct 2014 Location: Auckland Status: Offline Posts: 450	Post Options Post Reply Quote J-S Report Post Thanks(0) Quote Reply Topic: Valve mod - pcp pistol Posted: 12 Mar 2025 at 1:24pm
	That’s awesome.
	J S Airguns Air Arms TX200('s) Theoben Sirocco HW77 FWB 300s Webley Patriot One or two others... Current projects: Too many..

jwabfrog Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 13 Nov 2021 Location: Thames Status: Offline Posts: 152	Post Options Post Reply Quote jwabfrog Report Post Thanks(0) Quote Reply Posted: 12 Mar 2025 at 12:42pm
	Very cool Paul, you are a talented engineer!

Pauly5 Members Profile Send Private Message Find Members Posts Add to Buddy List Forum Moderator Joined: 11 Mar 2013 Location: Titahi Bay Status: Offline Posts: 1523	Post Options Post Reply Quote Pauly5 Report Post Thanks(0) Quote Reply Posted: 11 Mar 2025 at 10:06pm
	very firable now. I have completed the cocking lockup mechanism now and it's shooting really well. I fired about 6 shots over the chrony and got a fairly consistant 21 - 22 fpe from a 26 grn pellet. Next I am looking for a compact red dot/holograph sight for it. I won't make rails, but will attach the sight directly to the breech. Here's a link to a short video. https://youtube.com/shorts/naeNdHIvOVo?si=UgD87Ts6zoEL3e7s

RangerPete Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 19 Apr 2023 Location: Cambridge. Status: Offline Posts: 956	Post Options Post Reply Quote RangerPete Report Post Thanks(0) Quote Reply Posted: 09 Feb 2025 at 3:14pm
	Looking good, cant wait to see it when its all finished.
	Walk quietly, but carry a big stick.

Pauly5 Members Profile Send Private Message Find Members Posts Add to Buddy List Forum Moderator Joined: 11 Mar 2013 Location: Titahi Bay Status: Offline Posts: 1523	Post Options Post Reply Quote Pauly5 Report Post Thanks(0) Quote Reply Posted: 09 Feb 2025 at 2:47pm
	First bit of progress here for a while. I have made a start on what I call the cocking plate. This is part of the bolt lockup very similar to what I have done on another build. Bolt will be straight pull, but be spring loaded and will lock into and locate into place being held captive when loaded. It just a piece of mild steel, but I squared it up in the mill and countersunk the 4 screws that will hold it in place.

Pauly5 Members Profile Send Private Message Find Members Posts Add to Buddy List Forum Moderator Joined: 11 Mar 2013 Location: Titahi Bay Status: Offline Posts: 1523	Post Options Post Reply Quote Pauly5 Report Post Thanks(2) Quote Reply Posted: 16 Jan 2025 at 2:54pm
	Hi y'all, I got the lawns done tonight then went into the garage to do a bit more work on the pistol. I had been struggling trying to find a leak. At first I thought it was a line on the inside of the tube from production, so I honed it with 300 grit on a dowel in the lathe. It wasn't this, so I took a serious look at my O ring grooves and I had left a small ridge on the sealing side of it. removing this seems to have done the job. I reassembled the pistol and fired a shot over the chrony, and very interestingly it only read about 4 fpe. I figured this was due to it being too close because the next shot, from further away was better than I expected at a healthy 19.77 fpe. I still have to make the lockup device for the bolt/probe, so I am holding the probe in to fire. On the next shot I got 20.98 fpe. I have learnt that making sure there are no leaks in the transfer port area has a big impact on the power output and you can loose a lot of energy through leaks. I had cut a tapered lead into the barrel and I need to get a slightly thicker probe O ring too as it gets blown out of it's groove, so once I get that and the lock up sorted I am likely to see over 20 fpe for this .25 cal puppy. I don't know how accurate it will be, but I am very happy with the results so far. 26.23 grn pellet @ 600 fps

JasonEdward Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 22 Sep 2024 Location: Waihi Status: Offline Posts: 138	Post Options Post Reply Quote JasonEdward Report Post Thanks(1) Quote Reply Posted: 28 Dec 2024 at 9:07am
	Nice work - looks great!

J-S Members Profile Send Private Message Find Members Posts Visit Members Homepage Add to Buddy List Senior Member Joined: 20 Oct 2014 Location: Auckland Status: Offline Posts: 450	Post Options Post Reply Quote J-S Report Post Thanks(1) Quote Reply Posted: 27 Dec 2024 at 4:05pm
	It’s looking great! Healthy power too
	J S Airguns Air Arms TX200('s) Theoben Sirocco HW77 FWB 300s Webley Patriot One or two others... Current projects: Too many..

Pauly5 Members Profile Send Private Message Find Members Posts Add to Buddy List Forum Moderator Joined: 11 Mar 2013 Location: Titahi Bay Status: Offline Posts: 1523	Post Options Post Reply Quote Pauly5 Report Post Thanks(1) Quote Reply Posted: 26 Dec 2024 at 6:07pm
	I got a little bit more done today. Enough to fill and fire. I had been having trouble getting the poppet valve to seal. I was trying to get angles to match to no success so opted for a polished flat sealing surface which worked. Here's photo and it's first chrony reading. there's still a lot to do, but it's nice actually firing it now. Just over 15 ft/lb at around 1200 psi in 25 cal.

BC_Clark Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 16 Feb 2024 Location: Auckland Status: Offline Posts: 7	Post Options Post Reply Quote BC_Clark Report Post Thanks(1) Quote Reply Posted: 24 Dec 2024 at 4:11pm
	The main thing with drilling stainless is high feed and lower speed. It is not the heat that hardens stainless. Regular 304 and 316 are non heat-hardenable. They only become softer with heat. But they work-harden very readily (316 moreso). So applying too little pressure to the drill causes it to skim along the surface without starting a chip. This work-hardens the surface you're trying to drill. The problem with heat is that it blunts the cutting edge of the drill which leads to work-hardening of the stainless, accelerating the issue. HSS with cobalt can handle higher temperature.