I am 99.99% sure that it's just M249 and M240B - not different versions, entirely different weapons. By this logic the AK-47 is a bigger version of the M4 by way of caliber. If I am wrong, please correct me on the M249B thing, I've been out of the military for 9 years.
Is M249B a thing? You might be confusing it with the 240B (7.62 LMG)
The M249B is the smaller version. It uses the 5.56 rounds. The 240 is larger and uses the 7.76 rounds
I am 99.99% sure that it's just M249 and M240B - not different versions, entirely different weapons. By this logic the AK-47 is a bigger version of the M4 by way of caliber. If I am wrong, please correct me on the M249B thing, I've been out of the military for 9 years.