Regarding ammo deals, as mentioned, just gotta go early and see what the vendors are offering. I usually hit up SEC and Young Guns for ammo. Usually looking for 9 mm or 5.56/.223. Used to have more consistent sales before, but still can find good deals. But also gotta be prepared to carry the ammo.
I learned that carrying a couple of cases of ammo in a backpack isn't a good idea.
Regarding Armscor, I also have had meh impression of their ammo. I was going to buy up a bunch a few gun shows ago, but heard of problems. Then I experienced what seemed like inconsistent loading as well as a number of problems with function. While the problems with function can be the gun/mags, these guns ran fine on what I considered crappy ammo.