Thin barrels are very easy to dent. I have seen barrels pass proof at less than .020. I use to shoot a gun with barrels as thin or thinner than you are talking about. It is not as much how thin as where they are thin. A foot past your front hand is fine if between the chambers and your hand then that is another matter to me. Pressure drops slightly the further down the barrel you go from what I have been told. Highest within an inch of the chamber and much less near the choke area. Low pressure loads of the correct length should be fine.
