Unless you have the arms of a professional basketball player I can't imagine your left hand would be 8-10 inches from the muzzle unless your shooting a very short barreled shotgun.
Chamber pressure peaks closer to the breech and continues to drop as the shot charge travels further down the barrels. By the time its down towards the ends of the barrels (assuming 25 to 30 inch barrels), pressure has dropped a ton. Accordingly, the further you get away from the breech the thinner the barrel wall thickness can be. Barrel wall thickness will increase when one gets into the choke area. For Foxes and Parkers (gun's I know a bit more about) choke length is about 4-5 inches long.
In summary barrel thickness up near the breech area in front of the chambers are very thick. Normally at least .100. By the time you get to the middle of the barrels, barrel wall thickness should hopefully be in the .035 range. Most people would like minimum barrel wall thickness no less then .035. That said, many well struck barrels left their factories with less then that. I've seen some original Parkers that had untouched bores but minimum barrel wall thickness was in the .022 range. That was indeed down at the far end of the barrels, just before the barrels started to gain wall thickness due to choking.
PS. Above is my 2 cents and I freely except opinions very and many many more folks have more data/facts then I do.
