Fallout series

[Snekposter]

Yeah, the backstory for the White Legs is that Ulysses cracked open a big pre-war cache the legion knew about and taught them to maintain and use the guns inside. So they have to have some knowledge where to find these. It's entirely probable that they don't have much need for guns for internal patrols and warring against against tribals, so these caches could serve all their needs.

One of Ulysses's logs in Lonesome Road does mention Caesar's distaste for them, though.
https://fallout.fandom.com/wiki/Ulysses'_logs#Ulysses_log:_Y-17.23

The White Legs... meant to show respect, bribe me for Caesar's favor, echoing mannerisms and words... Showed them tech caches, taught them the workings of chamber and powder, spoke of Caesar's pride in those that used such things... lies.

I'd have to argue his stance is a reluctant pragmatism when it comes to any sort of large-scale deployment. After all, he's quite willing to blow up Kimball with a bomb or have a marksman blast him from the tower, and he's perfectly happy with the Courier if you reprogram the AA gun to blast him out of the sky as he comes in to land.