That’s pretty neat. I wonder how whoever got all those data points. I suppose it was done with one of those strain gauge thingys. Look to see the initial pressure rise. Although it still does not explain how they know the bullet’s velocity when it is at the 8” mark in a 16” barrel.
I had initially assumed that someone took a barrel and a hacksaw and recrowned the barrel at 16, 14, 12, 10, 8…. inches, but that’s clearly not the case.
I’d love to see a bunch of charts showing pistol rounds in various carbine and wheelguns (where the bullet and the driving gases need to jump the gap).
Strange thing is that the plots seem to be approaching asymptotic values which would clearly be wrong. Eventually, as the length increases, the friction in the barrel will be greater than the force of the remaining pressure on the bullet, at which point the speed should drop. I’d like to see data out past that point as a sanity check.