Modern star crimped shells are 2 1/2" long. So you won't feel any constriction when you dump them into the guns chambers. But open up to 2 3/4" when you fire them. In a 2 1/2" chamber, that extra 1/4" of plastic opens up into the bore of the shotgun, which is not relieved to receive it. Now the shot column has to be compressed into the bore past that restriction, and this jumps the pressure up to dangerous levels, especially in a damascus twist barrel.