I shoot several very thin walled doubles. It’s more where than how thin that I consider. I have a 20 bore that’s .018/.017 at 25+” where the pressure is much lower. It’s more a dent risk that a burst risk. Being reasonable is subjective but if my barrels are .025 out to 20+” I am fairly confident I can load and shoot ammo which will be safe and effective. Chambers need to be thick and pit free.
I once came across a Fox A grade 16 with ruined, pitted, chambers. Chamber sleeved it down to a 20 so it was a overbored 20 with 30” barrels. Made a great pass shooting gun. But with the original pitted chambers I would not shot snap caps. You decide your level of comfort and take reasonable measure.
