

Look in relevant locations to find ammo boxes.Sell unwanted ammo to buy ammo you need! Once you move on from using pipe weapons, you'll probably start collecting more pipe ammo than you can count - so sell it off for tons of caps and buy back the ammo you need.They can also grab ammo on their own if they are carrying the right weapons. If you don't want them wasting ammo, make them trade it back to you.

If you give them another weapon and have them equip it - they'll need consume ammo to keep using. Every human companion has a default weapon that they have unlimited ammo for. For example, having a Pipe weapon (with ammo that can be found easily) a laser weapon (with less abundant ammo sources) and a sniper rifle (rare ammo) lets you fall back to other options.
