I am not thoroughly convinced that shot doesn't react as much as a Semi-Solid as a Semi-Liquid when traveling down a barrel. I distinctly recall having read that in the early days of choke boring many barrels which were rather thin toward the muzzles had a problem of "Lifted Chokes", IE a bulge at the choke. This was not confined to the use of very large shot either. This would seem to indicate a Checking, rather than a speeding up of the charge. This seems to have been Fixed, by a slight beefing up of the wall thickness in the choke area. I have measured a good number of fairly light weight barrels in which the smallest diameter of the barrel was Ahead of the choke with a larger diameter in the choke area itself.
Also Burrard reported on some tests run some years ago in England wherein loads were measured for pressure, recoil & velocity simultaneously. Velocity was of course at this point of course the "Observed" velocity over 20 yards. A specially prepared barrel was made with a screw on forward end carefully lapped in to same diameter as the bore except one extension was cylinder & the other full choke. Length & weight were made identical. A definite relationship was recorder that the full choke gave a slight increase in velocity over the 20 yards, but also produced a slight lowering of recoil. This would definitely seem to be contradictory as the higher velocity should produce the heavier recoil.
This was explained by the cyl bore actually producing the higher muzzle velocity, but the quicker spread of the shot exposed each pellet to individual drag much quicker than from the full choke. The shot from the full choke reacted much more as a single projectile just long enough for them to exceed the velocity of the shot from the cylinder bore.
