Generally the unwritten rule is that the gun has to be a dmr platform in real life. I don't think a host would like you locking a mp5 on semi and running it as a dmr. Most dmrs are gonna be heavier and longer so its harder to maneuver. You also get a minimum engagement distance.
The point really is to conserve ammo firing semi only and act as a dm. Usually when I run my m14 I don't even finish off a mag unless its a long game.
Guardians of Asgaard - KF32
VFC H&K 416C
VFC KAC SR16 JL Billet SBR
TM FN Five-seveN