I haven't had any of the horror stories mentioned with UMC pistol ammo. I have used several CASES of it in 9mm in a variety of PISTOLS. However, I will state their .223 Remington rifle ammo is not very good. I was emptying a 30rd magazine of the stuff by pulling the cocking knob on my Sig 556 and one of the bullets was so poorly crimped it actually got pushed back into the case completely. I only noticed it because alot if the powder dumped out of the cartridge onto the carpet and made big mess. Also, it's accuracy isn't too great. Like I said the pistol stuff has been fine for me but the UMC rifle ammo was lousy stuff.
I will second (or 3rd, 4th, 5th and 6th), the America Brand ammo is pretty crappy too. I had one box of it in .45acp and it shot so inaccurately that I thought something lay have been wrong with a new 1911. Now, I run cheap TulAmmo through it (and other than being very dirty) it is extremely accurate.
IMHO some of the BEST practice ammo is Blazer Brass. Unfortunately, the don't sell it at my local Wal-Mart anymore and my LGS charges a little too much for it. The aluminum Blazer ammo works fine too. I don't reload. So, I'm not worried about reuse of the cases.