I'm running a Space:1889 game, and body armor is in use by players and NPCs. Leather is Def3, chain is Def5, and plate (helmets and breastplates) is Def7. Against firearms the defense is halved, rounded up (more protection) against pistols and rounded down against high velocity rounds from rifles and machine guns. All guns use black powder, although smokeless powder is available as a special invention.