Working on a game with gunsmithing as a primary feature, need some advice on how much wiggle room there is between bore diameter and projectile diameter.
Some basic context: The player might end up designing/building firearms from the very earliest hand cannons of the 11th century, to modern or near future firearms, though for this question I'm mostly thinking of contemporary firearms.
I know that even for modern manufacture, there's at least some variation between two 5.56 projectiles, even if they're from the same company and same batch. So I don't want to end up telling the player they can't use a given projectile/cartridge just because the one they want to load is 0.001mm too large.
On the other hand, I'm equally aware that 9mm Makarov is generally unhealthy for firearms chambered for 9x19 because the Makarov is actually 9.2mm.
So I'm trying to come to a middle ground that gives a result which "feels right" to most people.
I do actually have material stats for the projectile, jacket, barrel, and the barrel liner (if present), but using those to come to a solution would require a lot of math for what is a fairly narrow edge case. That's something that would probably be implemented post-release, assuming I ever get this off the ground.
So is there a known rule of thumb for this sort of situation, assuming a simple lead bullet with a copper jacket?