We would work accuracy nodes to get powder load for a particular projectile, then start with adjustment of the amount of jump to the lands of the rifling, then overall length. In .223/556, the bullet length would prevent fitting magazine, (max of 2.260") so they were for the bolt gun of course. Converted both bolt sniper rifles to single shot by installing an aluminum sled in the internal magazine.Yes, sometimes the gun club set one up, but long ago that I don't remember the numbers. I remember they were in the ball park.
What mostly we did was develop the optimum case/primer/powder/bullet combination for a given rifle and based our estimated velocity based on loading tables.
This is where Chrono becomes invaluable.
Bubba