Tell me, what happens if the bbl becomes completely blocked & the bbl explodes as a result of over pressure?
No more recoil. The gun just explodes.
If you look at recoil calculations, there is no mention of pressure which, longer forcing cones are supposed to reduce.
It is true that, pressure is the determining influence to a point, which governs the velocity of a particular mass at a particular velocity, however, the pressure is not the determining factor in relation to the recoil.
For example; a 22-250 50 grn projectile, fired at 3600 fps & 56000 psi does not recoil anything like a 12g load of 410grn at 10000 psi.
I presume that you think that the the length of the forcing cones effects pressure which, in turn effects recoil.
This could be said to be true if, you're a strain gauge & can differentiate in 10'000ths of a second, otherwise, the difference in felt recoil between a 2" & 4" or 10" forcing cone is, of absolutely no consequence.
All of the literature I've read by gunsmiths whom have expertise in shotgun forcing cones, bbls & chokes with, regard to pattern control, all recommend 2" max forcing cone length
All noted that patterns deteriorated when forcing cone length went beyond 2".
hope this helps.
Regards..............SoT