jasper
Rotten DM
and you missed ..If Colt then guns are common and simple weapons and we start out with a hand crossbow as base and change the range. If rifleman then Martial I use light crossbow for pistol and long bow for rifles....That's a fundamental failure to understand the problem.
Your first example involves a 10th level wizard which is something of a rare commodity.
Your second example involves a like 16th level fighter or ranger or something, which is even a rarer commodity.
Your third example involves a 0th level commoner. If suddenly every 0th level commoner can pull a semi-automatic handgun out and fire 3 shots in six seconds, that is not only game changing that's genre changing. That isn't even like super hard verisimilitude. That's just the implications of technology as opposed to magic. Technology democratizes power. There is no restriction on who can pickup a pistol and fire it to lethal effect. Even if your pistol is just a glorified rapid fire crossbow, the fact that anyone can fire three times in six seconds totally changes the dynamics of the game.
Even if all you are modeling are flintlock muskets, the gap between a 1st level warrior and a 10th level wizard just got a whole lot smaller. You don't have to be uber realistic. All you have is a one shot bang stick that justifies its existence by being a good bit harder hitting than a bow. If you get up to modelling modern firearms, a team of 1st or 2nd level hobgoblin fighters with modern weaponry like assault rifles, sniper rifles, grenades, and light machine guns absolutely is a threat to 10th level characters - whether in 1e, 3e, or even more so because of 5e's bounded accuracy.
So you get one trigger pull per attack.
So commoner is +2 to hit with is flintlock, colt, glock, M-16, .22 rifle. If COLt.
If Martial then a commoner is +0 to hit with his musket, colt, glock, m16, .22 rifle.
A mage is 9 th level caster with an 8d6 fireball. (Sorry I still stuck on 1E where level = d6) and looking at all the tier 2 modules, a mage is quite common.
If Martial then so call assault rifles have 10, 20, or 30 ammo before reloads. Range same as longbow.
If sniper rifle 1 to 10 ammo before reload. Range is treated same as longbow with no mod for long range.
Nades = fireball.
LMG will need discussion ...
TLDR. GUNS = BOWS with Loud BANG.