Their BBs have always been fine going through my guns (whenever I get my guns themselves working).
Like scarecrow said, there's plenty of reasons for jams. If you bring it up around other people, they'll probably jump in and help you take a look, or give you suggestions. UA's setup areas keep people pretty close together, and there's a plenty of experienced players amongst the casual players.
If the BBs weren't bastards, you could definitely put the BBs on the list of potential causes.