TomDoublePooch, rereading your post it sounds like you're not asking about low quality ammo, you're asking about difficult feeding ammo. I gather you understand they're not the same. Low quality, well, it can get as low as you like, and FMJ that's bad enough won't feed or work in anything. Now, assuming high quality factory or reloaded ammo, done right so any problems won't be a result of bad quality, there are certain bullet types that are more reluctant to feed. When I'm dialing in a 1911 I like to make sure it will feed a wide range of ammo, even in slow, hand-feed mode, and I consider the gun "there" when it will feed, from the top of a fully loaded Wilson/Rodgers magazine, these (be they factory or handloads):
-Speer 200 JHP "Flying Ashtray"
-Keith-style SWC, 215 grain, by National Bullet. Same loaded profile as the 240 Keith.
A gun that'll feed these will gobble pretty much anything, including any factory HP load, as both are rather stubby. 200 H&G 68 wadcutters are not such hard feeders in my experience. If a .45 ACP will feed 240 Sierra JHC's, well, even though they're not stubby, they have a ring of exposed, very soft lead at the tip. Very tough to feed. If your gun will feed these it might even take .50 Action Express!
The mention of Wilson/Rodgers mags is significant here.... they are a must if you are to have the most positive feeding possible.