Gotta go away for a couple days, but I see a couple of things that aren't quite errors but could use some clearing up.
Everyone is saying that the m4 and the mp5 have v2 mechboxes. This is true, but the Mp5k models have v3 mechbox.
Also m102404 talked about how difficult it can be storing the mp5 mags because of their length. However, Mp5 short mags are quite small, although of low capacity. They are roughly half the size of long mp5 mags; much like pistol mags.