Thursday, May 5, 2011

Crosman 338 Disassembly

I do apologize for not posting more, between work, kids and a terrible flu for the past few weeks I’ve been useless. Rather than posting nothing I thought I’d crack open a Crosman model 338 I bought a while back, just to see how it goes together. I’m still messing with the Crosman 105, having problems with it. In fact I’m only batting about 50% right now with airguns. Maybe I’ve lost my mojo or more likely I’ve been lucky up to this point. Possibly I need to stop playing with CO2 and MSP guns and crack open a springer…


It’s a copy of the Walther P-38.


The hammer is part of the casting, it’s not a replica by any means.


CO2 cartridge holds the right grip in via spring clip.


Hammer spring in the grip.


It’s stout, and a bit difficult to replace without levering it back in.


One screw for the left hand grip.


This exposes one of the two screws that hold the body together.




Things sort of spring apart at this point.


Safety on.


Safety off.


The barrel shroud and barrel lift out.


A setscrew holds the barrel lug to the barrel. This can be used to set headspace.


Everything somewhat sprung.


Other side of the riveted together trigger assembly and transfer bar.


BB shuttle mechanism.


Potmetal piece lifts out, notice the cutout for the passage of gas.


BB shuttle. There’s a small insert to take the wear of the trigger bar that lifts the shuttle.


Valve assembly.


Hammer assembly. Closest pin is the pivot, others are pressed/cast in place.


Standard piercing pin setup as found on most Crosman guns of this period.


The seal is worn. I replaced it but I’m still getting a leak right there (gas flowing out between seal and pin). Not sure why. Could be the latest seals I got from Crosman are bad or possibly I need to tweak something. This comes on the heels of a similar problem with the as yet unfinished model 99, so I am wondering what’s up. I never had such problems before. I’m sure I’ll figure it out eventually.


The 38 valve tool I made unscrews the valve.


Pretty simple. Not shown is the valve end seal – I left it in place.


Reassembled. Notice the position of the transfer bar. You have to sort of hold it in place while snapping the side back on, and use a tool to push it into alignment as you close it. requires 3 hands but becomes easier with time.


Notice the position of the transfer bar above the pin pressed into the hammer. Now I just need to figure out why the CO2 piercing pin seal is leaking...

Monday, May 2, 2011

An Aperture for the IZH Diopter Part 2 Final

Right back at it.

With the 1mm drill bit broken off flush in the aperture...

there was really nothing to do but drill it out with a solid carbide bit. Now the aperture had a giant hole. Lots of light! No sweat. I'll plug the hole and try again.

I opened the hole up a a little more with a #3 bit (my tapping size) and tapped the hole 1/4"-28.

Faced off a scrap of 0.250" diameter acetal (aka: delrin).

Cut a screwdriver slot.

threaded the outside 1/4"-28.

Chopped off a small section. Click the picture to enlarge it and it's easy to see the 1/4"-28 threads in the aperture disc.

A screwdriver from the front threads the acetal into the aperture. And I'm back to where I started before breaking the bit.

The acetal is in really snug and barely stands proud. It's not going to move under recoil so I don't have to worry about it vibrating out.

Faced off the acetal.


Lets try this again. Found another 1mm drill bit and through drilled the plastic plug.

The soft acetal was easy on the bit. Made a second pass at a faster speed. Wanted the hole as round as possible.

Blackened the face of the aperture with some Birchwood Casey Aluminum Black to minimize reflection/glare.

Blackened the inside of the through hole as well.

Test fitting.

Eye shade

All the clearances look fine. I'll paint the outside of the aperture.

A second piece of the threaded acetal rod was cut off, faced, slotted and spotted...

And through-drilled with a 1.2mm drill bit.

So, I screwed up, but ended up with a dead simple aperture with two interchangeable inserts. A 1mm and a 1.2mm.

Final shot. Wow, look at the size of that 10 ring! Just realized that these must be pretty old targets, as the scoring rings were downsized years ago.