My rule regarding Ultramax is the Nancy Reagan Rule: Just say no.
The only SERIOUS problems I've seen have been with their .223 ammo. A young friend of mine had an AR blown up by a round of their .223 that was evidently loaded with two 55gr. bullets in one case. That was a bit over a year ago, and they may have fixed their QC problems since then, but if I were going to use their ammo, I'd weigh every round before I shot any.I've got a couple of boxes of .223 sitting here. Only fired about 20 rounds of it through my Stag AR, with no issues so far. Never heard of any trouble with it until now.