I can't seem to get it to work. I gave the companion that comes with a .44 Magnum the Hunting Revolver, but he won't switch to using it.

You have to supply them with ammo.

I did, but he still didn't seem to switch out. Or do they wait until they're in combat?

Also, do they use up the ammo? So the only way for them to have unlimited ammo is with their default weapon?

The weapon you equip them with must have greater damage than their weapon, and ammo. Follower weapons are often "special" versions of the normal equivalents and do more damage than expected, so it may be hard to find something that replaces them.


Followers do use up ammo, but AFAIK, the weapon doesn't degrade while they use it.

1) Give them a weapon
2) Give them ammo for that type
3) Make sure you tell them to you either ranged/melee based on the weapon you want them to use. They could be set to melee, when you're trying to give them a ranged weapon.
4) They do use the ammo, but the weapons don't degrade
5) They will use the best weapon for both the situation and the best weapon with highest DAM, I've had a follower start attacking an enemy with incendiary long range, and switch to flamer for close range.

Even though Oh, Baby! is better than Lily's Vertibird sword, she won't equip the former when I put it in her inventory. I wonder why that is.

I wanted to do that too, but it didn't work for me either.... The Oh Baby is pretty powerful