No problems with either CCI or Federal bulk. Actually, mine has eaten about anything I throw in it, including tracers (just clean it really good!). I did have some trouble with some 80's vintage CCI but that was mostly poorly manufactured rounds and I guess quality control is better now. Of course, my usual range has a hissy-fit if you fire faster than one-per-second so I'm usually limited to flintlock-era firing speeds and that might allow for everything to stay cool (or bored to tears). Anyway, when I can let 'er rock I haven't had much trouble with the thing.