#3 I am in total agrement that under your scenario of plugging the bbl while recoil would be stopped the thrust against the gun would not only not be stopped, but rather increased. Agree, but I doubt increased.
R'Man; now just think about this one a minute, in this scenario you would obtain closed cell pressures. Certainly this would give higher pressure than an ordinary firing of the load.
#5 I am totally convinced that a 1oz 1200 fps load @ 10k psi will not load the gun as much as a 1¼oz 1330fps load @ 9k psi. This one is tricky. Where does the recoil force actually start? With the barrels? If so, then the rearward force of the barrels will unload the hook and hinge pin joint.
I can see no place for the recoil to start other than from the energy imparted to the standing breech from the back thrust of the shell head. The friction of the charge being pushed down the bore would in fact impart a forward motion to the bbls, but a lesser force than is being imparted to the breech. Many years ago in my National Guard days I fird a 3.5 Rocket Launcher & there was in fact a distinct forward pull as the rocket went down the tube, which of course was totally open to the rear. This same condition should exist in the shotgun bbl, but of course is un-feelable due to the offsetting effect upon the gun's breech. Thus when the charge is fired there are actually opposing forces trying to seperate the breech from the bbls.
Now I do believe we are mostly in agreement, with the exception of the part time plays in the mix. In looking at the peak pressure in available pressure curve drawings with the faster powders this peak is a virtual point, but with slower powders more of a rounded hump. Now I think we all know this peak of pressure will not compress a lead piston to the same extent it would be by a static load of the same pressure, thus LUP is lower than PE pressures from an identical load. Now the only real difference I can see here is the steel of the action is being placed under tension rather than compression.
If a 1200 fps load was given absolute uniform accelration & allowing for 29" of travel to clear the bbl then total bbl time would be .004 sec. Since acceleration occurs quicker near the breech actual time is more on the order of .003 sec. Now the top of that pressure peak is just a "Dot" on that 29" curve.
Yes I believe time does play a very important role in this situation. If it did not I do believe you would find a very large pile of destroyed guns, but you don't. If you calculate aformulas for strength of steels vs wall thicknesses, hinge pin shear, frame deflections etc, etc you will find many running on the Ragged edge, or over, yet they just keep on keeping on with loads far heavier than they were designed for.
While just a machinist & not an engineer I have studied everything I could come up with on this & similar subjects for about the last 40 years. I have come up with no other satisfactory explanation.
