Originally Posted by ThunderHockey
Petroleum based products and pressure are not a good match. I have heard (rumored) that in rare cases, they can combust, like when being used in air tanks.
Yeah, because in a tank the oils/greases can be subject to pressures in excess of 4500 psi, that's why you don't lube your tank regulator. Inside a gun, where the pressures are only a fraction of that, it should be fine. Vaseline will work, but it would be better to get a nice paintball specific lubricant. For your mech Cocker, just put some Gold Cup or KC oil on the o-rings and you'll be fine.