Well I thought I would add a bit this evening.
My 20ga damascus Flues gun has a thin spot of .018 @ 16" from the breach in the left barrel. I was really apprehensive about shooting it after this discovery, even with low pressure shells.
So, I figured what the heck, I would blow it up or shoot it. Loaded 4ea. hand loads @ 12,500psi per the IMR manual and did the string/proof/behind the tree test. I measured the barrels at a bunch of points before and after.
All is good.
Carry on. ymmv
Well . . .while you're likely safe with low pressure shells, 12,500 psi represents only a very slight pressure bump over SAAMI's current standard service pressure (max average pressure) of 12,000 psi for the 20ga. SAAMI proof loads run in the 18-19,000 psi range. Someone hearing that Damascus is safe with smokeless powder and not delving into the details might start shooting a bunch of Wal-Mart specials because they're "light loads" . . . and have a very unpleasant surprise.
