Author Topic: Semi auto PCP pistol (Read 23603 times - 2 votes)
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sb327 · « **Reply #140 on:** March 16, 2025, 09:17:49 AM »

I’ve enjoyed your adventure as well. Thanks for taking us along.

Dave

JPSAXNC · « **Reply #141 on:** March 16, 2025, 01:34:07 PM »

Thanks subscriber, It's an interesting design. Someone with some engineering knowledge and a drawing program could refine the design. I've built myself into and out of so many boxes I've lost count. It wouldn't be an exaggeration to say I've probably had the gun together and apart a 100 times. LOL. I don't see any reason that it wouldn't work in a larger caliber either, the little bit of air that escapes from the breech, could be eliminated by using a shorter barrel so all of the air could escape with the pellet. I don't know what effect that might have on velocity though, because I don't know if the pellet is actually gaining any speed in the 9" barrel. 680 fps. is the highest velocity I've gotten with the .22 CPHP's @3000psi. That's pretty low considering the bleed hole for the hammer is only .033 and the puff out of the breech blows a square of toilet tissue about 8" high. I almost have the new sear finished. Then I will try to refine the length of the bolt probe, in relation to the transfer port. It isn't easy because I can't see how far the hammer moves the valve stem and the hammer is carrying the bolt probe. Anyway it's still fun.

subscriber · « **Reply #142 on:** March 16, 2025, 05:35:43 PM »

James, with what you know, you would be in a good position to design and make another semi-auto pistol. I could be wrong, but a pellet probe that pushes the pellet deeper into the breech before the hammer strikes the valve stem my be useful, so the breech stays sealed longer on the return stroke. More efficient to loose 1/8 to 1/4" of effective barrel length from the rear, than lopping off more than that from the front. This has to do with the relative velocity and travel distance of the probe/hammer VS the pellet.

The snag is that your total hammer travel seems limited, because the probe needs to take a bit of a run at the mag to push the pellet out and still have energy left to produce a good hammer strike. Anyway, that is just what I think I have picked up from your journey.

JPSAXNC · « **Reply #143 on:** March 20, 2025, 09:58:09 AM »

I got the pistol back together, the new sear works fine and the trigger is a little nicer. I noticed when I was fitting the sear that the lever that engages the sear was pushing up on the sear as the lever moved back causing the trigger break to feel stiff I fixed that. Also the hammer rests a little further back on the new sear so I had to make a new bumper for the hammer to get the timing right between the hammer bounce and the sear reset.

JPSAXNC · « **Reply #144 on:** March 21, 2025, 10:18:59 AM »

I spoke to soon about everything working again. It's not a bumper problem, I've tried different bumper lengths and I'm still getting double taps. I had to make a new lever for the sear, to get the sear height right and made the slot in the lever to deep. The sear and lever work the way they should, but I think the sear is pushing the transfer bar down a little further so the transfer bar has to travel a little further to reset the lever. I'll see if I can sort it out?

JPSAXNC · « **Reply #145 on:** March 22, 2025, 08:06:40 PM »

It's working now. I started a 2" shorter barrel for it so I could if and what the difference in velocity is like.

JPSAXNC · « **Reply #146 on:** March 26, 2025, 10:51:34 AM »

I have an issue with my bolt pattern. Three equally spaced screws, one on the bottom and two near the top allow the valve to tip slightly under pressure. Would one on the bottom and two centered on the side, keep the valve straight? TIA

subscriber · « **Reply #147 on:** March 26, 2025, 07:42:00 PM »

James,

I would need to see a picture or sketch to answer you bolt tipping question. Generally, to reducing axial tipping, you would want to reduce slack at the front and rear of a bolt, rather than just one ring of screws.

JPSAXNC · « **Reply #148 on:** March 27, 2025, 07:56:27 AM »

Hi Subscriber, It's the firing valve that tips. The firing valve is long because of the projection on the back of the valve that the hammer rides on. The clearance between the diameter of the projection and the ID. of the hole in the hammer is small. So any misaliment will cause the hammer to drag on the projection. Since the valve is held by two screws near the top and one screw on the bottom, and the screw pattern is close to the back edge of the valve. The valve wants to pivot under pressure like a seesaw. The screw hole spacing is 60 degrees so I drilled and tapped for two more screws opposite the top two screws near the bottom, so now 4 screws are holding the valve and the valve should remain straight. I'll find out today.

subscriber · « **Reply #149 on:** March 27, 2025, 08:10:15 AM »

Adding stabilizing screws to the valve sounds like the smart thing to do.

JPSAXNC · « **Reply #150 on:** March 27, 2025, 06:59:27 PM »

Valve is centered now, the hammer moves smoothly along the projection. After that I noticed quite a bit of drag from the new sear, I've about got that dialed out.

JPSAXNC · « **Reply #151 on:** March 30, 2025, 05:31:05 PM »

I worked on the sear to where I could use a little less sear spring tension, But then I had to increase the distance to the bumper to get the sear to latch. So new plan, The vent hole in the valve for the hammer was .033 I made a new insert with a .026 hole to see if I can slow the hammer down a little as it moves back.

subscriber · « **Reply #152 on:** March 30, 2025, 07:52:33 PM »

James, you define patience and tenacity.

JPSAXNC · « **Reply #153 on:** March 31, 2025, 11:53:22 AM »

I had finished the shorter barrel, it was 2.1" shorter. The velocity dropped by 10 fps. per inch. So the longer barrel was still using the air. I didn't know if it was. I reduced the hammer vent hole in the valve from .033 to .026 and got a surprise, not only did the hammer still cycle, the velocity increased about 40fps. I didn't imagine that the air loss to the hammer was that high!

JPSAXNC · « **Reply #154 on:** March 31, 2025, 12:34:25 PM »

Here's a string 50cc reservoir 3000psi fill .22 14.3 grain CPHP's 679 672 678 676 672 673 669 672 668 672 668 665 667 660 662 658 660 654 654 650 652 651 645 643 640. 26 shots. This is Viper territory with a 1300psi. lower fill pressure.

Nvreloader · « **Reply #155 on:** March 31, 2025, 01:39:11 PM »

JPSAXNC,

I just finished reading about your exploits for this build, Very outstanding job,
FWIW, I read that you were having problems with the hammer spring etc.
I have been converting all my AG to the FLAT WIRE spring, full power in a very limited space, a 24#, 5" long FWS will go coil bound in 1.50" when fully compressed.

These springs come in numerous pound ratings and several different OD diameter,
mist all come with .250" I/S hole diameter, there are recoil spring for the PB semi auto pistols, see info here:
https://www.ebay.com/sch/i.html?_nkw=flat+wire+recoil+springs+&_sacat=0&_from=R40&_trksid=p2505460.m570.l1313
HTH,
Tia,

JPSAXNC · « **Reply #156 on:** March 31, 2025, 02:44:30 PM »

Thanks Don, Yeah the problem was a long spring in a small space. The set length of my spring is 2 1/4" it has 12 coils of .043 music wire the id. is .406 the od. is .5, I wound it at
5 coils per inch this gave enough power. At the same dimensions and six coils per inch, it was to weak.

JPSAXNC · « **Reply #157 on:** April 03, 2025, 05:21:23 PM »

Well shooting it is kind of disappointing, The long barrel plus the recoil is throwing the shots high. The sights I have on it are maxed out, I have an old red dot I could try.

JPSAXNC · « **Reply #158 on:** April 04, 2025, 01:26:42 PM »

Different fix, I just made a new blade for the front site about .1 taller, now it's perfect.

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Semi auto PCP pistol

Author Topic: Semi auto PCP pistol (Read 23603 times - 2 votes) )

Author Topic: Semi auto PCP pistol (Read 23603 times - 2 votes)
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