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Pistol build
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Pauly5 View Drop Down
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    Posted: 11 Oct 2023 at 9:55am
Over the past couple of months I have been inspired to build a pcp pistol. I do plan to build a breech, but at this stage I am basically converting a Crosman 22XX from CO2 to HPA using the trigger frame and steel breech.
Inspiration to do this is from a couple of very clever people that have given me good advise and the recent purchase of a small vertical mill has rocketed my confidence in build quality.

This won't be a long thread, but you should get the general idea of what i've done.

I started looking at other designs in both the big bore and lower power design. The possibilities and concepts rattled around my brain for a while and I started off planning to use the std valve system that came in the 22XX.  I ended up using a bigger sized tube, and so I had to make my own valve and hammer system.

My main concern in all of this was safety. So after getting all the info together I felt good about what I was to do with a 3  x safety factor for retaining the pressure. With this sorted it gave me a base to work off.

I didn't know what sort of performance the pistol would produce, but I have been pleasantly surprised and now have a base to work off for future build and refinements.

Photos show a few different stages including my trial and error parts. I basically built the pistol twice. This was a good idea as it meant the finished item had minimal adjustments made to it, and my measurements are recorded, so each build will be quicker.

Photo to come in another post. Thought i'd get the words done and dusted first. I will also share a bit more detail about it's performance too.
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Pauly5 View Drop Down
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J-S View Drop Down
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Pretty bloody cool..
J S Airguns
Air Arms TX200('s)
Theoben Sirocco
HW77
FWB 300s
Webley Patriot
One or two others...

Current projects:
Too many..
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Pauly5 View Drop Down
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Posts: 1410 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Pauly5 Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2023 at 10:27am
So my first fill was around 1800 psi and I shot it down to around 800 psi.
I used JSB 18.13 grn pellets.
33 usable shots and quite a gentle power curve. The variation between shots jumped about, but as I was shooting this string I was shooting groups and on paper it was a dead rabbit every shot.
Hopefully in the future I can refine this with trialing different spring tension and addition of a hammer tension adjuster to balance the valve and hammer. Shot string copied below.

1568
2586
3565
4563
5568
6586
7596
8588
9584
10608
11616
12622
13622
14607
15640
16622
17639
18614
19612
20641
21623
22641
23632
24621
25616
26613
27608
28598
29584
30582
31566
32559
33540
AVG600.9090909

I'm not after perfection, and to me it's a victory so far enjoying shooting it. I have teamed this up with a cheap hand pump and it only takes 50 strokes to fill to around 1800 psi according to the gauge on the pump. It's turning out to be a good little combo.
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kruzaroad View Drop Down
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Posts: 2284 		Post Options Post Options   Thanks (0) Thanks(0)   Quote kruzaroad Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2023 at 5:13pm
Looks awsome.
Why did it take 9 shots to hit the 600fps mark?
Ave for first 9 shots = 578 fps
Ave for next 17 shots at (600fps +) = 658 fps.
Thats a 80fps gain.
Like wise the last 6 shots
Ave =571 fpe (no calculated decimals but was 571.5)
Is a 87 fps drop.
The drop off at the end I understand.
The ones at front I don't.
If it's just it needed time to settle in I'd say you'd be closer to 650fps.
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Pauly5 View Drop Down
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What the numbers show is typical of a non regulated pcp. Also called the power curve. That's what the grapgh shows. A regulated shot string is in theory a flat line until it drops below the reg pressure,

What is happening there is that the tank pressure (1800) is a littler bit stronger than what the current valve/hammer set up can use, so it isn't hitting hard enough to release full energy. Once a few shots are fired and the pressure drops, the hammer can open the valve longer giving a higher pellet speed. So if I filled the tank to say 2500 psi, it would likely have even lower initial speeds.
If I want to utillize higher tank pressure I will need a stronger hammer tension.


This tank is quite small, so I feel that to get 30 + good shots means I have been lucky with this setup.

The variation in the spread between shots can probably be reduced with refining of the firing parts.
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kruzaroad View Drop Down
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OK that makes sence.
Do you have stronger hammer springs?
I got a few when I got them made up for 362. Didn't use the strongest. Still have 3 i think of differnt strengths.
Let me know if you have trouble finding any.
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Pauly5 View Drop Down
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I plan to get some, but I can also put an adjuster in to create more tension. The more power I get, the less number of useful shots, but it's a case of seeing what happens.

Lots of avenues to develop.
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kruzaroad View Drop Down
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Posts: 2284 		Post Options Post Options   Thanks (0) Thanks(0)   Quote kruzaroad Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2023 at 7:39am
So what's the weight of the pistol?
And where is its point of balance?
The hammer spring tensioner sounds like good idea. Not only as you could increase the tension but you could reduce it for indoor/around structors bird shooting. Which I imagine would be a bonus in your line of work.
Be keen to see a review of your mill at some stage too, if your keen.
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RangerPete View Drop Down
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Posts: 884 		Post Options Post Options   Thanks (0) Thanks(0)   Quote RangerPete Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2023 at 1:06pm
Pauly, what about fitting a reg, like the huma you put in my little Elly?
That should flatten out your power curve nicely, maybe even give you a few more shots.
Walk quietly, but carry a big stick.
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