Marushin mossberg m500 leak (NOT AN O RING PROBLEM)
 

I bought a used m500 and everything is fine except when I fill it up with propane (using a mad bull adaptor with silicone oil), most of it comes right back out the blowout valve and the filling valve, and i only get 4-5 shots. I checked the orings, and they are perfectly fine. Am i filling it wrong? Are the valves broken (where can i get replacements)?

The o-rings may have shrunk. Try soaking them in a bath of silicone oil to swell them back up and try it then.