I think I'm confused here. I thought this post was about shooting 2 3/4" shells in guns originally chambered for 2 1/2, 2 5/8 shells etc. Obviously different loads will make a marked difference. I was assuming we were talking the same shot and powder charge.
My experience was with identical ammunition and different chambers. When you change loads, all bets are off.
Dick the discussions on recoil, felt recoil etc. have raged for years but the simple truth is that recoil is governed by Newtons Third Law of Motion which simply put says that for every action there is an equal and opposite reaction.
So long as the total ejecta weight, exit velocity and firearm weight remain constant recoil energy will remain the same no matter what the hull length is, no matter what the chamber length is, no mater what the forcing cone angels are and no matter what the bore size is.
Here is the formula for calculating recoil:
E= 1/2(Wr/32)(WbxMv+4700xWp/7000xWr) squared
E= energy in foot pounds
Wr= weight of gun in pounds
Wb= weight of shot and wad
Mv= muzzle velocity in fps
Wp= weight of powder in grains
You will notice that there are no allowances for chamber length, chamber pressure or anything but gun weight, ejecta weight and muzzle velocity.
