MarkB
Legend
The entire point of guns is to kill someone before he comes close. In a D&D/HP system that is simply not possible. You can set up any amount of level appropriate ranged combatants and barring environmental obstacles like cliffs you will never be able to kill someone before he can punch you in the face.
That changes the usage of guns completely compared to real life.
A CR3 Archer from Volo's Guide to Monsters fires twice per round, and deals an average of 8 damage per hit. If the person advancing on them has a low AC, which a character in a Western setting will, they can take down an average-HP character from a 3rd level party in two turns - so, unless their opponent wins initiative and is close enough to close the distance in one turn, yes they can kill them before being punched in the face.