Didn't mean to step on any rubber tails.
Interior ballistics, or what goes on inside the chamber at firing until the bullet leaves, is a very complicated subject involving mathematics for which I'm not all that serious about.
It's somewhat a black science even to the experts at the major cartridge companies. Terminal ballistics is much the same and continually argued about by people from different scientific disciplines.
The only field of ballistics that isn't THAT difficult for me is exterior ballistics for which the above links refer. This, of course, simply involves what happens to the bullet from the time it leaves the barrel until it hits the target. Calculations are long winded differential equations, but I got hold of the derived formulas some 25 years ago from an article in "Rifle" magazine by a New Mexico State PhD in mathematics and wrote my own BASIC program to run on, first, my Timex Sinclair toy computer and later a "high tech" Tandy Color 3 which has a whoppin' 128K ram.
Seein' as I'm no Einstein, that speaks to the simplicity of exterior ballistics modeling, but interior ballistics has many more variables that are much harder to measure and model and I don't know that there is any computer model written even today that a moron like me could use for any useful purpose. It's a heck of a lot easier just to go to the range and shoot the freakin' load over the Chrony, and besides, it's more fun.
If there have been advancements in the art of modeling interior ballistics, there's probably someone here a lot smarter than me that could bring us up to date. It's something I'd thought about for about 10 minutes until I began to realize the futility of trying to understand it.
I think I gave 60 bucks for it and they ain't much more'n that now.