Originally Posted by
GoatBoy
You want the urethane for the moving seals. The power tube o-ring is probably one of the more important ones to have in urethane, more so for LX bolt.
This holds for most things. The LX actually works really well with buna but it does wear out quickly. The softer buna reduces bolt stick issues due to having a carrier that is a tiny bit too tight.
Originally Posted by
GoatBoy
For something that's static, like the outer on-off o-ring, I don't see why that one can't be buna. It's the inner one that gets the movement, and that's why that one is teflon.
The teflon is in place because it doesn't harden when it freezes when CO2 passes by it unlike urethane or buna.
Originally Posted by
GoatBoy
However, seeing as all that o-ring is doing is keeping the thing off until you release the sear, I don't really consider it that critical. It can leak a little bit, and all that means is your chamber gets a little more air, or your LX might start venting. Hell my current mag has a tiny leak down the barrel when I hold the trigger down. It's not like I run around with the trigger held down, so I haven't even bothered to change it out, and it hasn't affected me.
It is quite critical. If this oring leaks it causes bolt stick issues. The tiny leak you hear when you hold the trigger is caused by residual pressure in the chamber leaking out past the carrier oring because the vent hole is really close to the bolt stem vent hole and you are using a perfectly fitting carrier. If you have shims installed, removing them will probably make the leak go away. It goes away when the trigger is released because the additional chamber pressure on the oring tightens it up.
Originally Posted by
GoatBoy
The last time I saw a problem with that outer on-off oring, it was simply because the o-ring itself was badly manufactured -- there was a visible defect on it. Maybe the previous owner had recycled a Q/D o-ring and threw it in there in a pinch. So if you did see a problem with non-urethane, don't automatically assume it's just because of the material.
What I have yet to see data on is how long the various materials actually wind up lasting in a gun. I think that's where you'll be able to really calculate the tradeoffs.
Its not always about life of the oring. Urethane is stiffer than buna. If you look at the elasticity of the two types, buna has much greater elasticity than urethane. Urethane also has a larger pressure rating. If there are large gaps to allow air flow when a passage is opened, buna can get pushed out of place easily but urethane will stay in place. In these situations, buna will get pinched and leak.
Except for the Automag in front, its usually the man behind the equipment that counts.