Benjamin Gunnar - O-rings

[CK]

I had a leaky Benjamin Gunnar, I think it was the regulator.  Benjamin/Crosman doesn't have a diagram on their website but I found a manual for the Reximex Nyx which is almost the same (Reximex was OEM for the Benjamin Craftsman line).  https://reximex.com/wp-content/uploads/2025/02/NYX-.pdf

Posting these to help those who have one so they don't have to guess on the O-rings. Sorry for the format, this is a copy & paste of my spreasheet and I don't have the patience to format using the table function....

I couldn't find some of the metric sizes easily but found dash (-) substitutes that worked.  The dowty seals I found substitutes: AceFlux Dowty Bonded Sealing Washer, for M12, 7/16", -4AN Threads. https://www.anhosefittings.com/dowty-bonded-sealing-washer-m12-3-7-16-4an.html

Durometer   ASTM   Cross Section /Thickness   Inside Diameter   
70      1 mm   3 mm   Poppet 2A-004   
70      1.5 mm   3.5 mm   Regulator high side (2A-003)   
70      1.5 mm   5.5 mm   Breach seal (chamber)   
70      1.5 mm   6.5 mm   Transfer port adjuster (2 ea) 2A-051   
70      1.5 mm   8 mm   Barrel to receiver (2 ea) 2A-014   
70   -115   2.62 mm   18.25 mm   1   Benjamin Gunnar   Regulator block to receiver (2A-055)   -115 (3/32” cross section11/16” ID, Danco #13) substituted and works well
90      1.5 mm   4 mm   Bottle valve stem 2B-008   
90      2 mm   4 mm   Regulator adjustment 2B-009   
90      2 mm   6 mm   Bottle adapter   
90      2 mm   9 mm   Regulator low side (2B-017)   
90      2 mm   9 mm   Bottle valve (rests inside bottle to seal against bottle adapter) 2B-017   
90      2 mm   19 mm   Regulator block 2B-031   
90   -110   2.5 mm   9.5 mm   Poppet spring cap 2B-053   Olypsys grid measured to -110, CS 0.1”, ID 0.36”
90   -116   2.62 mm   18.72 mm   Bottle valve main seal 2B-030   
Dowty   1.5 mm   12.7 mm   Tank seal (1 ea) and bottle adapter seal (1 ea)

For the Foster fill nipple valve, the listed o-ring for the stem didn't seal well for me.  I replaced the entire fitting with an M10x1 off of Amazon.  I removed the Gunnar factory seal, which was probably a mistake.  The factory seal turned out to be a delrin-like seal atop a small brass dowty seal (probably one for an M5 screw).  The replacement while teflon seal that comes with these cheap replacement nipples was too thin and soft.  I tried reusing the dowty beneath it but no joy.  I'm currently testing the seal with a spare from my JTS Airacuda, that's working better but time will tell.  If you Foster isn't leaking don't mess with it for now.  If it is leaking, then try to keep the original seal.

I did not replace anything in the bottle valve itself.  That thing is over torqued and I'm not going to mess with it for now.

Word to the wise, limit the number of times you pull the bottle off while pressurized.  The bottle adapter threads are soft, and I saw a lot of wear.  So I started degassing.  Needless to say I've used a LOT of air on this reseal messing with the foster that I should have just left alone.

[CK]

I forgot to include that the list is for a .22 caliber rifle.  I think the only difference for the .25 caliber would be the breach seal O-ring