The Repair skill allows you to maintain any weapons and apparel. In addition, Repair allows you to create items and Guns ammunition at reloading benches.

Repair is still good in New Vegas, for many of the same reasons. There has, however, been one significant change to how the skill works. You no longer need to get your Repair skill up to 100 to repair an items condition to 100… the higher your skill the more you repair when you combine an item, but if you have enough of them you’ll be able to fix an item to your heart’s content. Also, some weapons and armor are prohibitively rare, making fixes with Repair difficult (unless you have the Jury Rigging perk). You need a whopping 90 Repair Skill score for this, but there are other considerations, too. You’ll need 50 Repair to make Weapon Repair Kits (restores 25% of an equipped weapon’s condition, which is just great for fixing all that rare expansion gear you bring into the Mojave, or vise-versa), and you’ll need a 70 Repair score to get the Hand Load perk… which you can use to make .308 JSP ammo, which turns the Gobi Campaign Scout Rifle into the Finger of God.