It is marked on the top of the barrell XL Shot-gun 44 Cal. (Antique status as produced in 1885).When a 44 mag. round is loaded into the tube with no problem and also the locking block to come closed and rdy for fire.The fired brass at the barrell end measure 2/1000 th of a difference.Cycles the empty clear for a no problem quick fire.
He isn't firing the damn cartridges, just mentioning they FIT.
ps I just ran a dozen rounds of 44.Remington Magnums and it works great other than the sore sholder.