Manu-Arm Air Pistol Disassembly, Part 2

On I go…

The cocking bar, that part of the cocking linkage that pushes the piston back.

I don’t know why it has that square bit. Possibly a sort of anti-beartrap? Hmmm.

One trigger pin pushed out.

The sear is odd, there’s a ball bearing on the sear and one on the piston.

The trigger and its two pins.

I couldn’t remove the “cocking body”.

The pin just wouldn’t come out more than this and I did not want to destroy the gun.

The rear sight.

A setscrew locks the plug to a cross-pin.

I was too lazy to drag out my spring compressor so I just used a bar clamp. The spring does have a significant preload.

Pushing the cross-pin out

The end plug. Notice the integral cruciform spring guide.

The piston.

See the ball? Shiny ball

.

The piston seal is a simple slug of molded elastomer. I forgot to take pics but it has a groove on the underside as it’s molded. I think an easy replacement would be an aluminum slug with an o-ring.

All the parts…

Here’s a poor shot of the two sear balls in contact, representing a cocked condition. When the trigger is pulled the one ball slowly rotates out of contact, which yields a sliding motion as the sear releases. Not crisp, but smooth.

Anyway…reassembly is exactly in reverse. I took some time to properly lube everything. The gun does shoot smoother than before.

Manu-Arm Air Pistol Disassembly, Part 1

A while back a request was made to take apart my Manu-Arm air pistol. Finally got to it.

The box.

Pistol and drawing.

Drawing.

Instructions.

.

It’s not a bad looking pistol, for all the potmetal and plastic.

One screw through the grip.

And two screws on either side into the action.

The housing comes apart typically.

Notice the trigger adjustment screw.

There’s a dowel pin loosely in that grip hole to align the grips.

The action removed.

A view of the action…

And another of the trigger…

Break the barrel to relieve tension.

Remove the pivot screw. Notice the steel washers on the pivot bearing.

I punched out the cocking linkage pin. I was very cautious when knocking out pins as most of the parts are potmetal and could break.

Barrel removed. More to come…

Copy of Anthony Rienecker's Pro-Top Part 2 Final

I'm back at it here and almost done with the valve front.

Drilled a seat for the valve spring.

Finished it with a flat ground drill bit.

Here's the guts of the project. Elected to use a brass mesh filter screen washer like some of the old Crosman guns.

After assembling the valve, I scribed a witness mark across the halves. This lets me disassemble and reassemble repeatedly to the same location. Why is this important? Because I'm only going to notch the valve body for clearance on the front grip frame screw. Rienecker solves the problem nicely with a relief groove.

Excuse the marks on the body. Got the gun used and that's what I found inside. Strap wrenches, rubber or leather-lined vise jaws, nah. Slip-joint pliers or pipe wrench! (sigh)

Installed the valve in a 2240 gas tube. Dropped in a 12g cartridge and screwed the endcap down. All the way. Bottomed. No go.

It doesn't go any further.

Missed it by that much. The cartridge is literally a few thou from piercing. Well, pretty close for all the guestimating. Failed to account for the valve setting backward in the gas tube due to the sloppy head fit of the 6-40 mounting bolt and forgot about the CO2 cartridge seal stretching before piercing. On the plus side, it's easier to fix this than if the valve front was too long...
I reinstalled the same cartridge tightened the cap then smacked it with my palm. The cartridge pierced. It was that close, but that's not enough wiggle room for different cartridge brands, lot variances, wear, etc.

Easy fix. Add a spacer to the gas tube cap.

Found a scrap of W-1 drill rod.



Turned down one end to press fit into the inside of the cap.



Squeezed it together in the vise. The maple block prevents marring the end cap. I was gonna use the pipe wrench, but then...

Way too much spacer. Only need a few hundredths.

Chopped most of it off with a hacksaw.

Then faced it down. (Opted for a press fit as I didn't want the possibility of dropping the spacer outside in the weeds during a hasty cartridge change.)

Done.

Last item--Need some space to screw the front grip frame bolt into the tube. The front of the valve needs to be relieved a bit (how much depends on the screw length). I marked the spot with a sharpie.

A center cutting end mill in the drill press made the notch.



With the added spacer, the cap has 100% thread contact and plenty of adjustment range for all the 12g cartridges out there.

I'm on the fence about posting velocity numbers and shot counts. Largely because they aren't going to necessarily represent Rienecker's production Pro-Top and I don't want to take anything away from his idea. He was kind enough to humor me to (badly and sort of ) copy his work and write this up as I saw fit. Honestly, I was impressed that he even returned my email. After working with this design for a couple weeks now, it seems that this should be the Crosman 22XX valve standard rather than the piercing pin design they currently use. The only single advantage the stock valve has is that it's self-piercing by virtue of the striker firing the pin into the cartridge. I look at Rienecker's modification and see a tuning tool. It increases valve volume, and can support less striker spring force if you want a higher shot count. Conversely, you can also use a heavier striker spring and not have constriction from the pin. The benefits are there for both low powered shooters wishing to get a few more consistent shots as well as for the power mongers looking for a few more fps. I just don't see any real downsides.

Anthony Rienecker can be contacted here for additional information about his Pro-Top valve:
amriensr@yahoo.com