Originally Posted by Kozzie
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 long range and accuracy at long range. Range is related to your hop-up unit, your hop-up rubber and your barrel bore and length, these will also have an effect on your accuracy.
Exactly, Better quality will get you accuracy and range.