One interesting thing about the .410 is the SAAMI Maximum Average Pressure for the 3" shells is 13,500 PSI--which is higher than for any other shotshell except the 3-1/2" 12-gauge, where the MAP is 14,000 PSI. All the others range from 11,000 to 12,000.
I doubt this would be much of a factor in thickness of the rear of the barrel, but have always found it interesting....
