The sheet I use is only .3mm thick but can withstand around 70-80 P.S.I.
It's funny, you can put a disc in and fire at 0x (normal combustion) And the disc does'nt burst, it now looks like an old ww1 helmet!
Now put in two shots of fuel and CRACK! Works a real treat.
It should be good for at least 5x mixes

Now wheres that stungun.............
Peace
Scotty
The size of the discs are 1 1/4 inches in diameter (custom union)