I am neither a physicist nor a Dr, but I think this is a rather complex thing of which there are varying opinions. Many years ago Burrard reported on this subject a series of tests done by, as I recall, one of the Major British Ammunition makers. Test bbls were made up with precisely fitted extension tubes so that all factors were identical except for choke or lack therof. The bbl was fitted for pressure checking (crusher), velocity recorded per standard British measurement of the time (IE observed vel over 20yds) & recoil "Measured" (NO Feeling depended on) in a pendulum gun.
Several differing loads were checked & results were extremely consistent & Amazingly while the full choke always showed a slight increase in observed velocity the recoil from the choke showed a very slight, probably imperceptile by "FEEL" reduction.
The only plausible explanation they could come up with was that there was a slight check as the charge hit the choke restriction, accounting for the reduction in recoil. The velocity gain of the choke was accounted for by the shot being held closer together acting somewhat as a solid projectile for a bit upon exiting the muzzle, thus individual pellets not taking on independant drag characteristics as quickly as from the Cyl bore.
While I understand the Venturi effect Rocketman describes (the reason the carburator on an old 2-cyl John Deere can pick up its fuel) from purely a laymans concept it seems reasonable to me that when the shot charge hits the choke it might not immedialy take on this attribute being more solid than either a liquid or gas, but would indeed receive a check in its velocity. As the individual pellets jocky for position from the reduced area they would then begin to take on this effect but not necessarily regain all that had been lost from the initial checking.
This then leads to my next question, in the 20s/30s just how close to the muzzle was Remington able to ontain accurate reliable velocity measurements. Only a very short distance would be required to account for the results the British obtained.
