Sorry I'm so late to this conversation. I've had some experience with bushing tanks and with burst disks so I'll add my two cents in case there's a nugget that might be of help. Like you, I got a lot of help from the guys on this forum so, I might be repeating something they already said.
Paintball Burst Disks
- I'm interested to know if you got the 1800 psi paintball burst disks to work properly. I tried some a few years back and they didn't seem to be made for our vintage valve sealing method... My valves have a flat sealing surface and the paintball units are kind of like volcano orifice?
- I was never able to find any 1800 psi burst disk units. But I got some modern 2015 psi one piece units that go for flat seal scuba. I got them from Dive Gear Express. They're labeled to release at 3360 psi which is 5/3rds of 2015 psi. DGX says install them torqued 100-120 in-lb. Before I got a torque wrench, I used to install them snug, Then fill them full pressure and check for leaks by dunking. And if they leaked, I would gently tighten just until the leak stopped bubbling.
Sealing Bushing Tanks
- I've found that it's really important to clean the threads on these old tanks. In addition to rust, they may have hard residue from the old pipe dope method of sealing that was originally used. They may also have sand or abrasive residue from internal cleaning. I have scrubbed these threads with a toothbrush sized stainless steel brush using hot water with Dawn detergent and then scrubbed some more while rinsing.
- I DO have a home made strap type tank vice made from steel strapping and a 6 foot 2x6 board.
- I DO have a big box wrench to fit the bushing flats and also give good leverage.
- Finally, I've had very good luck getting these bushing tanks to seal on the first try.