You’re right in that all of these numbers are best case scenarios. In battle, someone is shooting back. Plus, you have tons of variables to control besides the shooter, including powder quality, cast weight of the mass-produced bullet, wear or leading in the barrel. Heck, even the amount of powder you spill as you hurriedly bite off the end of the cartridge can matter."...a regiment of 1600 men at a hit rate of one in sixteen would cause 100 casualties per volley. A regiment of 1600 men firing at a hit rate of one in 150 would cause ca. 12 casualties per volley; this means that a brigade of 4800 men firing at a hit rate of 1 in 150 fighting a regiment of 1600 men firing at a hit rate of 1 in 16 comes to:
Regiment inflicts 100 casualites (1/48 of enemy strength) and takes 32 casualties (1/50 of own strength).
This above hypothetical goes completely out the window because it doesn't allow for receiving incoming fire from an enemy equipped with the same arms and with the same field strength. The number of casualties inflicted on both sides diminishes exponentially with each shot/volley fired. Thereby radically changing the percentage of rates of hits to a much lower number with every shot fired! These numbers, rates, and percentages, remind me of the military warfare video games the grandkids play with!
Sure, a sharpshooter/sniper is alone and far more careful, and his hit rate is much higher, but we’ve moved into the battle line. All bets are off there. Your chances of hitting at any distance, at least intentionally, would be fairly low in the face of round shot, buck and ball, and fixed bayonets.