KalNet Message Board

I understand this thread has some age on it, but so does my VM!
So in keeping like information together, I present my o-ring findings.

O-ring list:

Part Number Qty Part Name
CH-4 1 ( 4) O-Ring
VMS-231 4 Upper Bolt O-Ring
VMS-252 1 Lower Bolt O-Ring
VMS-302 1 O-Ring

Valve: CH-4
015 U90 Urethane O-ring
O-ring Size: 9/16"ID X 11/16"OD X 1/16"CS
CH-4 -- same o-ring as on the valve, also same o-ring as used in the front Bottle Plug Adapter Assembly cap on a VM-68 Magnum… so…… Tank o-ring!
AND~~~ Stock brass barrel with threaded collar the buffer o-ring…? CH-4!!!


Upper Bolt O-Ring: VMS-231
stock bolt o-rings from Pro-Team Products - VM Bolt o-rings
3/32 thick 7/16 i.d. appear to be 70 duro Buna-n

I have found this -> Old PGP Bolt O-rings:
111 (70 polyurethane)
O-ring Size: 7/16"ID X 5/8"OD X 3/32"CS

Palmer's Sells Viton for the Bolt.
O-ring Size: 7/16"ID X 5/8"OD X 3/32"CS
111 V75 Viton Fluorocarbon Brown O-rings


Lower Bolt O-Ring: VMS-252
Also known as the Hammer o-ring, a.k.a. ‘the one you cannot get’.
Check with Bacci or Palmer's


O-Ring: VMS-302
This o-ring seals the Bulk Gas Adapter assembly to the front of the body.
Provided your were crazy enough to want to take that off in the first place. Yeah I did because I like taking things apart.

208 U90 Urethane O-ring
O-ring Size: 5/8"ID X 7/8"OD X 1/8"CS

I also replaced it with a 90 durometer urethane o-ring, I am thinking a 70 would have worked just fine as I had a bear of a time getting that hard 90 into place. And tightening it down, boy howdy you could feel the resistance in the o-ring. But it did not bulge out nor pinch that I could see.




A little more about o-ring materials for the upper bolt o-rings, that I found out about when I was putting o-rings on the bolts of my PGPs:

I asked Palmer's why they offer Viton o-rings in their kits, rather than the polyurethane suggested in other posts:
Craig Palmer
We chose longevity over friction.

Viton has more chemical resistance and withstands higher temperatures. We found that after a while, if paint was left on the bolt, the o-ring would swell and lock up the gun. We also found that people would leave the gun in a trunk of a car during a hot summer day and flatten out polyurethane o-rings. Also Polyurethane has a shelf life of 5 years, Viton is 15 years.

If the bolt was under constant pressure then polyurethane would have an advantage.

We use polyurethane in pressurized cyclic applications or anything that receives more than 200 psi on co2. The pulse of air on the bolt is less than 100 psi.

We do stock the bolt o-rings in polyurethane if you need them.

The above reasons is why we developed Delrin flat rings.
__________________