Manu-Arm Piston Hijinks

I decided to try making a replacement piston seal that uses an o-ring for the Manu-Arm pistol.

The Seal seems to be almost exactly 25mm.

The underside of the seal.

The screw. It has a 90 degree head…

The piston face.

Drilling some delrin. I ended up using a #4 drill which was the closest I had to the 5.25mm shank of the screw. I turned the body .976”, later ones I turned to .984”. Greater diameter leads to more o-ring support.

Countersinking. The only 90 deg countersink I had was too small…

So I set a boring bar to 90 degrees and plunged in to make the countersink. After this I found a 90 degree spotting drill that was perfect, used it on the rest of the piston seals.

Grooving for an o-ring. I was aiming for about .005” over 5mm with the o-ring installed. But I only had a 116 o-ring and it lost diameter when stretched. Later pistons seals used #118 o-rings.

It shot about 360fps, which was slower than the 426 I got with the original seal. So as I mention above I made some more seals using 118 o-rings, and played with diameters and groove depths. Current seal I have installed is getting between 428 and 436 fps, which is slightly better than the stock seal. So the design works fine.

Seals…

You can see the difference in groove width & diameter. The left one is the current successful design. Both have #118 o-rings. At some point I’ll actually follow the procedures Parker recommends and grind a proper tool, etc.

Beeman R1/HW80 Caliber Change

I'll cut to the chase as I'm time crunched today. I have a .22 cal Beeman R1 (HW80) and I wanted to convert it to .25 cal. Long story involving having a .25 cal R1 years ago, the gun was stolen, couldn't replace it with another .25 cal at the time so I bought a .22 cal and...blah..blah..

So, after almost three years of looking, I was finally able to pin down a .25 cal barrel/breech block last week. The replacement Weihrauch barrel assemblies don't come with a cocking lever arm attached. The cocking arm is riveted to the bottom of the breech block. A spare rivet is not provided--but can often be ordered. I opted to not order the rivet.

No pics of rifle disassembly as we've covered it before here. I pounded out the rivet holding the cocking lever to the .22 cal breech block and set the .22 cal assembly aside--maybe for good.



Often, the rivet can be reused, but not this time. The pin has a 5mm shaft diameter.

Lacking a piece of metric drill rod, I turned down a piece of 0.250" W-1 steel to the required 5mm diameter. Actually, it needed to be 4.99mm.

Cut the new pin a few thousandths longer than the width of the breech block.

Used a file to bevel each end into a slight dome.

I've seen a couple one-off replacement cocking lever pins that have used e-clips on each end. That looked like it would require widening the slot in the forend of the stock. Too much work for a guy like me. Figured there was another way.

Center punched the breech block.

Didn't bother to fixture the breech. I lined up and drilled through with a #36. Not shown: Tapped the hole with a #6-32 plug tap.

Filed a small flat on the pin for the set screw to bear against. This will lock the pin in position yet make it easily removable.

Breech block, pin, set screw and cocking lever. What more could a guy ask for?



Blued the pin with Birchwood Casey Permablue paste.



Set screw snugged down. Lucked out on the length of the screw. It's flush with the block. I like this more than the factory's method of assembly.

Done! Reassembled the rifle and now I can work my way through those thousands of .25 cal pellets that have been mocking me on the shelf. Should I ever want to revert to .22 cal, it's now a ten minute swap with the replaceable pin.

Something else soon.

Making a Safety for a Crosman 22XX/13XX

Looked at the safety on the Crosman 22XX guns many times and marveled at their simplicity and ease of use. For all it is and does, it's hard to make a case for something different. Nevertheless, I craved something else--probably because I have too many 22XX guns...

Started with a piece of 0.500" diameter 12L14 cold rolled steel.

Turned the body of the safety to 0.186".

And added two grooves for the ball bearing detent.

Turned down the end for the button head.

And cut off.



Test fit. Note: No trigger yet. Just eyeballing some dimensions, making sure it's reachable, and looking at it for a sense of balance and scale.



Started hand filing the notches.

Compared it to a stock Crosman safety and just filed away until everything matched up.

Uhhhh, done?

Test fit #2--with the trigger and sear installed.

OK, OK, so it's not done. The head was too plain. Clamped with some aluminum to protect the piece.

I didn't have a metal checkering file so I improvised with a thread restoring file. Used the 20 tpi side...

and patiently grooved the head.

Deepened the grooves with a small riffler file.

Test fit #3...

Blued with Van's.





Installed the safety (actually the entire grip frame) on a 2250 project gun.





It's a nice change from the standard safety and I like that it doesn't stand out. It looks just like the magazine release on old Colt series 70 .45 Gold Cups.

More stuff soon.