problem with gun

[flamerz14]

I just assembled my marble ammo ripper system(MARS) four hours ago. It uses a 750ml aluminium bottle as a chamber and 2 feet of 1/2" as the barrel, actuated by a ball valve. the mouth of the bottle does NOT fit NPT threads(i used copper fittings) so i tried epoxying them.Apparently while filling , the epoxy cracked(although cured) around the mouth and schrader.causing zero pressure..Any ideas on how to join the mouth to a male thread adapter?

EDIT: webcam pic of the leaking scharder and the screwed-up fitting that i broke off.

[spud yeti]

That sucks, maybe if you silicone it, there will be less chance of cracking, but thats just a guess. How much does it not fit by?

[flamerz14]

I have a 0.5" fitting from the ball valve.. but the bottle opening is just under 0.75".Is there something threaded i can use for increasing 0.5" to 0.75"? And i used cheap two-step epoxy instead of industrial steel epoxy.Could this be the cause of it breaking on my schrader too?

[spud yeti]

Well, you could look for a reducer, and adapt it to fit. You should use the industrial epoxy, its much better for strength if you ask me.