Actually, 4570guy is wrong. In season 4 episodes 7 & 8 (Into Hell Part 1 & Part 2), Mac, Grey, and Bob have M4A1/CM203 combos. These are my two favorite episodes that I have DL'ed on my PS3 and I watch them obsessively. I'm positive they're fake because they all have cocking handles on the left side of the receiver.