I didn't know it was expanded length! I never measured a shell. The math will still hold true, I'd imagine.
Both fed as well as state wardens here carry a marked up rubber hose. They shove that in the shotgun magazine tube to measure if you can hold too many. In the past they would ask you for a few rounds of the ammo you use but have apparently dropped that - they told me they don't want to drop your $3/round shell in the mud and fiddle with guns and ammo with their "customers".
I never felt the need to touch off more than 3 at a time. By the 4th round I am sure you mostly blow up $ and no more ducks.
G