Semi auto PCP pistol

[subscriber]

Thanks for the detail, James

[Rob M]

the hammer recoil with a 1/16th hole will be violent.. My last semi auto ball shooter didnt even have a dedicated hammer bleed hole , it easily cocked the heaviest hammer spring i had.. ( i just oversized the stem hole a few thou, and that was enough) its actually quite amazing how reliable this simple design is , barring any pellet and mag jams. Its part of the reason crosman 600s are soo relaible

[JPSAXNC]

Hi Rob, If the 1/16" hole is to big, I'll press a plug into it and drill a smaller hole. Yeah, with the o-ring sealed hammer It might a bit much. Another issue might be Hammer lock up, there's only about 1/16" from the sear latch to where the hammer bottoms out. If the bounce is to violent it might be to fast for the sear to catch the hammer.

[Rob M]

it will probably be fine assuming the sear has enough spring to return in rapid fashion.

[sb327]

it will probably be fine assuming the sear has enough spring to return in rapid fashion.

I agree. You don’t want a very big window there because it will be too rough on the sear.

Dave

[JPSAXNC]

I assembled the pistol, charged it to 1500psi. and tried it a couple of times. The velocity was very low and the hammer bounced and didn't go back far enough to latch. The hammer has good force going forward. I had put in a super heavy valve return spring, that seemed the likely problem. Because I recharged it and it hadn't used hardly any air. I put in a lighter spring and will test it again tomorrow.

[JPSAXNC]

The lighter valve return spring didn't make any difference, low velocity and a little bouncing same as before. So I suspected the hammer was compressing air so I removed the o-ring sealing the hammer. Recharged to the same pressure and got a long full auto burst, but still no lockup. So the hammer was definitely compressing air. Now the dilemma, The id. of the hammer is very close to the od. of the back of the valve. So the hammer is still probably compressing air because the velocity is still very low. So I can turn down the back of the valve a little to help vent the hammer but how much of a reduction would be to much. The back of the valve is .495 od. and the id. of the hammer is .498-.499. What's your best guess?

[rsterne]

Put a bleed screw in the back of the hammer to tune the leakage?....

Bob

[JPSAXNC]

That's a good idea Bob, but the hammer is to hard to drill and tap. I took the gun apart again and saw an issue with the valve stem, I left it to long, so the low velocity could have been due to the pellet blocking the transfer port, because the hammer carries the probe and if the hammer doesn't go far enough forward neither does the probe. I tweaked the clearance on the valve body a bit and will try again tomorrow.

[rsterne]

Anneal the (back of the) hammer?.... Use a small torch, heat the center to dull cherry and let it cool slowly....

Bob

[JuryRigger]

Very cool and excellent work!!
Watching 
Jesse

[JPSAXNC]

I might be making some progress. Today I realized that the hammer was not vented in the tube so it was compressing air on the valve and in the tube. Also I discovered that the hammer was not going fully forward, when the breech was attached. I'm going to open the clearance holes in the breech for the screws one size. And ink the pin and the slot the pin rides in to see where it's rubbing if that is the problem.

[Rob M]

dont vent , its likely not the issue.. if anything add bigger hammer spring

[JPSAXNC]

Hi Rob, There was a number of things I had to adjust. I just tried the gun again at 1700psi. The velocity was 520fps. but the hammer did not go back far enough to latch. I'm pretty sure the hammer spring is to stiff for the hammer to latch. The problem is that when the hammer is cocked, there is only about .540 clearance between the back of the hammer and the end cap. And I have to fit a spring into that space that can then send the hammer forward 1.2". I'm going to wind a spring with a bigger diameter so it won't be as stiff, and see what happens.

[Rob M]

good to hear velocity is sorted out.

[JPSAXNC]

The velocity. I assumed that the barrel I grabbed was .22, it took 4 weeks to notice it wasn't.

[JPSAXNC]

I'm trying to get everything to move as smoothly as possible. The bolt probe was a little off center and rubbing on one side of the breech. I bored the holes for the barrel and probe in two separate operations. So I made a mandrel to go in the barrel bore, and using a small boring bar trued up the bolt probe hole. It feels like I need to make the o-ring groove in the breech of the barrel a little deeper, The probe goes in a little tight . I want just a little contact. I'm winding a hammer spring, I made three but there a little weak. I'll try one more.

[subscriber]

Sounds like you are on the right track, James

[JPSAXNC]

One more attempt to wind a spring today, 8 coils per inch was still to weak I'll try 6 coils. Another issue is the finish on the hammer and in the tube, both are turned on the lathe to polish. The hammer would slide more smoothly if one surface was polished linearly. The bleed hole I made in the valve for the hammer had to be positioned so that it came out in the transfer port, the valve throat is to small to make the hole in line with the throat. The problem with that is the transfer port is smaller than the valve throat so there's a big pressure drop in the transfer port so the hammer doesn't get enough push back from the air. Yes, I could drill out the valve stem hole larger to get the air in line that way but I would rather not because when there's free play on the valve stem the valve does not open and close exactly the same every time and hammer energy is lost due to the free play.

[JPSAXNC]

Finally over the hump, the new hammer spring was the magic pellet. The vent hole in the TP. worked just fine, I'm getting too much return pressure now, it goes auto and then latches.  So I'm thinking of plugging the vent hole and drilling it out very small, and then increase the diameter if needed to get the best balance? What do you think?