Semi auto PCP pistol

[JPSAXNC]

I have an idea for a semi auto pistol. I have a grip frame from a Benji 422 it has a semi auto trigger and sear. I could attach it to a tube. The firing valve and hammer would be a copy of the Crosman 600 valve and hammer. The 600 valve and hammer have a big advantage because the hammer is sealed to a projection on the back of the valve. requiring only a tiny amount of air to cycle the hammer. The hammer and bolt would be connected together with a pin so the hammer would carry the bolt forward and back. The disadvantage is that the pistol would be long because I would need 7" of reservoir from the back of the fill valve to the front of the firing valve. On the plus side, the barrel would be long. Also on the plus side the overall profile would be fairly low, like a 2240 using a jet magazine. The overall length would be about 13". It's all in my head right now but I can see a good possibility it would work. I'm going to order a tube and 7075 aluminum for the valves.

[JPSAXNC]

I ordered the materials we'll see how it goes.

[sb327]

I’m not familiar with the parts exactly you are using but it sounds interesting and I’ll be watching.

Dave

[JPSAXNC]

The Benjamin 422 is a co2 semi auto pellet pistol, a clever design with a sketchy magazine and feed system. The Crosman 600 is also a semi auto co2 pellet pistol, more mechanically complex than the Benjamin. I think both of these guns could have benefited from the spring loaded rotary magazines we have today. That's what got me thinking about building one.

[JPSAXNC]

I got my materials but I'm recovering from pneumonia. It's to cold for me to go out to the shop for now.

[JPSAXNC]

I made a sketch of where the parts will go it's looking good, almost a lego gun. This coming week it's supposed to be warmer, I'll cut some metal.

[rsterne]

Looking forward to seeing it.... Your projects are always interesting....

Bob

[Habanero69er]

Following.

[JPSAXNC]

I have started work on the valve and tube. I'll start the hammer and will finish polishing the tube ID. today. So this gun is a combination of the Jet hammer and bolt probe stroke lengths, it will use a Jet magazine. The Crosman 600 style valve will use the Jet style poppet and seat, because it's very easy to open, and the Benjamin 422 grip frame. It's a bit of a challenge to get every thing lined up on paper, so I'm making all of the parts to get a better idea of how they will fit together.

[JPSAXNC]

I have to remake the hammer I made a mistake on it. But other wise I think I have the position of the parts worked out so everything lines up. Still more work to do.

[JPSAXNC]

I have the grip frame attached to the tube, I had to make and braze a lug to the tube like on the 422 tube. I made a stem and poppet for the valve, still have to make a front half for it. I haven't worked out a hammer spring for it yet, the back of the hammer is very close to the end cap and the hammer needs 1.185" of travel.

[subscriber]

James,

To minimize hammer weight loss use a small diameter spring, running in a central channel that is drilled in the middle of the hammer from the rear of the hammer.  Small diameter springs are stiffer than large diameter springs, so can be made to take up less space.  With a small central channel almost all the way through the hammer, you end up with a mostly external guide for the spring.  You can use a central guide acting on the rear spring ID that is short enough not to contact the hammer spring tunnel at full cock.

Of course, I could be talking nonsense about your system, because I have not seen the parts you will be using, or their dimensions.

Images or sketches of your planned system with dimensions will help.

[JPSAXNC]

Hi subscriber, If you google Crosman 600 Schematic you can see the hammer lay out. The only big issue I have is that I needed  the hammer to have a stroke length .2 longer than stock. I think I can still squeeze in a hammer spring.

[subscriber]

So, the hammer and spring are pretty much defined.  Remaking them to enable a longer hammer stroke might be opening the top and bottom of a can of worms

[JPSAXNC]

Oh yes! But I think I have the can of worms figured out. I'm inching my way along.

[JPSAXNC]

Well I made a mistake. I'm ok at visualizing the big picture but some times miss a small detail in between. I was adjusting the clearance between the sear and hammer, but the hammer was feeling draggy over the sear because it wasn't hardened yet. I had already made the threaded hole for the pin that will attach the hammer and bolt probe together and forgot about the hole for the cocking handle which I hadn't made yet. And went ahead and hardened and polished the hammer so I could get the best feel over the sear, and only after realized I forgot the threaded hole for the cocking handle. I drilled the hole with a carbide bit but could not get a thread to cut even with a chrome clad tap. A carbide 4-40 tap cost $90. so threading is out. I redrilled the hole to 1/8" and will use a dowel pin for a handle. Otherwise it's coming along.

[sb327]

Would it be possible to drill oversized, then loctite some material in that had been drilled/tapped?

Dave

[JPSAXNC]

Thanks, That's a really good idea.

[JPSAXNC]

I'm over the hump as far as getting the parts to fit. I still have to make a fill valve and end cap for the bottom end. When the bottom end is finished I will start on the breech, I'll make it out of aluminum. So far so good.

[JPSAXNC]

I got a little more work done, I threaded the back of the tube and made a plug for it. I'll make a bumper for the end plug to stop the hammer. I have to wind a hammer spring for it, a small diameter spring won't work because there is no support for it. It just buckles, a larger diameter spring will work. Then make the fill valve.