We played a Milsim game in Petawawa a couple of weeks ago, and Sepulcrum's 416 was too hot (about 415). So he used my SAW most of the day. After a few hours of lugging that behemoth around, he wanted something lighter. We went back to the van to switch guns, and he loaded his Madbull BBs in my mags, went to try to adjust the hopup before going back in the field, but they totally jammed up the mags.
I don't know why, but the Madbull BBs jammed up in all my AK mags - the stock 150 round RS mag, and my 5 King Arms 110 round plastic mags. I've fired KSC, Metal Tech and Bastards out of that gun and never had any problem with any of them. Only the Madbulls ever caused a problem.