what would be the best guns to use on a Salvador running on the brawn skill tree that have high ammo running in the base game (non DLC)
Brawn tree? Take a look at the Deputy Sal build/gear for starters.
Deputy builds require so little skill points to work that they are perfect to dip into Brawn. As VH101 points out.
Otherwise, Brawn builds lack the extra firepower of the Gunlust tree, so they have to compensate by using more powerful guns. Anything with through-the-roof DPS is a good match. Usually, shotguns are the answer here, but there are other good choices too.