TargetTalk

Looking for the "O" ring sizes for a FEG GPM CO2 Pistol model 1 or 2.
Measuring the old o rings is not an option, very swollen and broken.

which o rings

35/ Ball sealing ring
42/ Bolt o ring
43/ Tank body o ring
65/ Valve fixing screw o ring

Being CO2 i susspect they need to be green vitron seals, nitrol will swell badly.

Generally, the best material for CO2 is polyurethane. Viton isn't a whole lot better than nitrile as far as CO2 absorption is concerned, but in both cases, it depends on the exact polymer formulation. There are special formulations of decompression resistant O-rings in both types of material.

Walther used to use polyurethane in their CP-1 & CP-2 O-rings.

With the pistol stripped down, now looking for FEG parts.
A source of a tank ball and ball seating ring.

since you have the pistol apart, measure the O-rings, I.D, O.D. and thickness, and go to McMaster & Carr and order them. You will have to order a pack of 100, but the package will probably cost less than $5.00/ pack. I had to order replacement O-rings for the buffer on my Pardini SP-1 and the cost was less than $4.00 foe 100. I only needed 13 for the pistol so I"m set for life on that.

Mike

O rings are not the problem any more, the tank ball seat seal is the problem.
Tried to use a O ring instead, worked once then blew out. Fail...
Cannot locate a source of parts.
One mfg. in China wants to make me 7000, I don't think so......

Sounds like you may need to find a friendly hobbyist with a lathe. Before they could be ordered directly from Czechoslovakia, I machined a couple Tau-7 firing seals out of nylon.

Is the old seal still intact enough to measure? One problem with the Tau-7 seal was that it was a press fit, and once extracted, I had no way of knowing how big to make the OD. Once I got some real ones, I determined that I had made them slightly undersized, but they still worked.

One other modern option for such projects is "Maker Spaces". For a monthly membership fee, you can get access to a lathe (and other tools) & if needed, instruction on how to run it.

If the seal is some sort of rubbery elastomer, life gets more difficult. You may have to mold it. Another option is a small run prototyping service. Just as an example, these guys:

https://www.quickparts.com/

Can make cast urethane parts, which could be better than the original.

I recently bought some o-rings from
https://www.theoringstore.com/store/
Low minimum order and large variety.
Hope this helps

Looks like the next trick is to turn one up.
I have a lathe and mill, just need to get some acetal rod about 8mm,
and some very sharp tools for clean cuts.