Generally speaking an M4A1 will get more distance than with an MP5. This is because it has a longer barrel, a CQB type M4 will have a similar sized or shorter barrel and will tend to have the same or less range.
Now there is a difference between range, and accuracy at range. Range is related to your hop-up unit, your hop-up rubber, your barrel bore and barrel length, these will also have an effect (but aren't the only factors) on your accuracy. So a shorter barrel gun can out range and have better accuracy than a a longer barrel gun if it has a nice TB barrel, hop rubber and good compression.
** edit: Note FPS doesn't have as much of an effect on range and accuracy as most people think.
Last edited by Kozzie; March 14th, 2012 at 15:05..