Pressure vs Recoil;
While the statement often made that recoil is caused by pressure "Is True", it is also "Equally True" that pressure is not a factor in determing recoil. Factors in recoil are the amount of weight being moved & the speed with which it is moved.
You can for instance with proper powders load a 3" 20ga with 1Ľoz shot & push it out the muzzle at some 1250 fps with pressures no higher than another load using a very fast powder pushing 7/8oz to some 1175fps. This equals 3/8oz more shot @ 75 more fps.
Now you have only to fire both of these loads from a gun of about 6lbs wt to see which has the most recoil, though both have essentially the same pressure.
Now which of these loads will stress the frame the most?? My vote goes for that load producing the heaviest recoil, but I know of no way to prove it except to place a gage which will measure the stress applied across the juncture of the standing breech to the bar. I do not have the equipment to do this. Most of this "Flexing" back of the standing breech is produced by the back thrust of the shell against the breech, not by the flip of the bbl.
