Chief, those magnums were factory deals. I don't know whether the monobloc was any different. Maybe long enough in all of them to accommodate 3" chambers. It'd be interesting to compare. But I'm only talking about guns that came from the factory with 3" chambers, not those that started life at 2 3/4" and have been lengthened.
SAAMI pressure standards are the same for 2 3/4" and 3" 12ga loads, so assuming the same shot charge and velocity, there should not be much difference in recoil. Pressure has far more variables, but they'd both have to be within the SAAMI standard of 11,500 psi.
