Well, here's the way to prove it to yourself once and for all. Now, who said that the Physics books were gospel? Seems to me, they avoid things they don't understand.
Lock a .45 acp pistol down in a Ransom Rest, pointing parallel to the ground and out over a patch of desert, where you can see the point of impact. Fire a reound with a H&G 68 bullet seated normally. Note impact point. Fire a similarly loaded round with the bullet seated backwards. Note that the flat end forward round hits the ground closer to the muzzle, thus proving that the bullet is aerodynamic when fired point end to. If you are really curious, obtain the NACA aircraft cowling outlines of 1929 from the Wright Pat Museum and compare them to Elmer Keith's 173 grain swc .38 special bullet. (Lyman 357429) Did he know what he was doing? Oh, yeah!
This is dangerous, but it resolves the debate once and for all.
We used a Florence style pyrex flask, mounted in a horizontal position with a bunsen burner under the round side of the bottom of the flask. Look through a box of new solid rubber stoppers until you find one that is a fairly tight fit in the neck from the start. Push it down into the neck until you have about 3/8" to 1/2" of bearing. Draw a line around the top of the neck position on the stopper. Then, sandpaper the topmost postion after wrapping sever wraps of tape around the bearing surface to the mark unti it will slip fit in the "bore" of the flask to the tape.
We used an old Bolex 8mm camera that took a 400 foot reel of film. (You only get to use 200', since you have to reverse the reels for the second half. Set at slow motion (64 frames per second.) Use a long cable release, a double thick sheet of plywood with a small window and a transparent section of thick lexan.
Watch the setup until the stopper begins to move and cramp down on the cable release.
Now, this is nothing like "real time", but proportionally, it is correct (who said "you can't scale nature"?) and when you have replayed the film for the umpteenth time, you will see the stopper speeds up appreciably when it exits the "bore" of the flask neck. It would help to place a sheet of cardboard behind the neck and in front with 1/2" spaced vertical lines to get a better appreciation of the differences in speed. You have a slow beginning, a faster exit and a marked accelleration.
This is dangerous, since the power of steam is nearly beyond imagination, but we did not have a tragedy using new Florence flasks and new stoppers.
And, none of this answers the original question, because a chronograph will not read muzzle velocity, but instead reads the shock wave of the report.
And, this poses the Zen question: "If nobody is present in the forest and a tree falls, does it make a crashing noise?" Answer: "No." When nobody is present, there is no phenomenon that we call "sound". It requires a receptor eardrum to convert the compressed air waves into perceptible sound, as it requires a radio receiver to convert the waves of a radio signal to audible sound when they reach your ear. (Not a precise analogy, but close enuf fer Gummint work. Again, let the skeptics rage. I have told all I know 'bout Newtonian Physics down a rifled tube.
In the final analysis, what difference does it make? It is still those little round (we hope) holes in the X ring that count. And, lotsa guys have fired millions of rounds without worrying about the physics involved. Just enjoy it.
Which, I guess, brings us back to cheating by slipping a rifle cartridge in a Lewis gun and quoting Savage. "30 to 35 feet per second accelleration past the muzzle due to impinging escaped gases."..unless somebody else can quote something different.
