Seems to me they would have to use a very fast powder with 5/8 oz of shot to get the pressure up to 11.5K psi. What would be the purpose of this high pressure with such a light load of shot? I would suppose it so they will "Kick" an Auto bot back, but as most autos, in use, today are gas-operated it seems to me a slower powder with a lower "Chamber" pressure would maintain a higher barrel pressure down where the gas port is.
As a dyed in the wool double shooter I see no advantage to a shell that short anyway. I did a search on the Federals & seems they only load them with a slug, buckshot & 15/16 oz of #8 shot. The slugs & buckshot I would guess are aimed at law enforcement, don't know who the # shot load is aimed at.
