Tonight, we will take a look at some basic expansions to facilitate OSR combat in a modern setting. This mainly means firearms.
In general, a basic hand gun or simple hunting rifle will inflict the basic 1D6 damage.
Military grade weaponry, like high calibre military rifles will inflict +1 damage.
Weapons capable for burst fire may target 2 opponents near each other (up to say 2 meters apart), rolling to hit against each target individually.
Firing a burst against a single target permits a reroll of a failed attack roll, but no additional damage.
Against larger than man sized targets, resolve 2 individual attacks.
Grenades and similar explosives (like a stick of dynamite) inflict 2D6 damage with a saving throw versus Breath weapon for half damage.
The monsters in the night:
Monsters can generally be divided into several categories regarding how they react to damage.
Mortal monsters will take damage and die, like any other character. While they may be resilient (in the form of armour class, hit points or saving throws), they are ultimately mortal.
Resilient monsters are often from other realities or otherwise beyond normal physics. They only suffer the minimum possible damage from any attack. Simply assume that every damage die scores a 1 automatically, unless a 20 is scored on the attack roll.
Impervious monsters cannot be harmed by mundane weapons. Magic or special implements must be employed to bring them down, if possible at all.