I shoot doubles with walls as thin as .018-.020 on a fairly regular basis. I am very strict about what loads I use and keep the pressures down to sane levels, 8,000 psi for 20 and 5,000-6,500 psi for 12's. The important thing to know is where are they thin and what your real pressure is on the load you want to use. Barrels at .020 are more likely to dent than blow up with sane loads. Thin barrels 20" from the breach do not scare me but anything less than that or closer than tat will need careful consideration before I shoot them. Very careful.