SpudFiles

On my copper pnuematic the chamber has started leaking. It's a 3/4" BSP thread and I have used PTFE. It can only do another 1/2 turn before it is too stiff to tighten more, and I can't keep it like that because it ruins the orientation of the cannon. It never used to leak then about a week ago it just started.
Any ideas what might have caused it or what I can do about it?

Sounds like the thread pitch is warping (so to speak). Are you breaking it down and reassembling it over and over? If not, try liquid thread tape and let it cure before pressurizing. Worth a try.

I scraped off the old PTFE and wrapped some new stuff on and it has mostly done the job, I can now leave it for 5 minutes and it'ts acceptable (but I never do) so I won't sacrifice the manouvreability of being able to dissasemble it. Thanks though

It can still be broken down while using the liquid thread tape, it just fills the gaps better, the down fall is the curing time. What isn't directly exposed to air takes longer.