Sounds like that ARs are only for bodyshots. That's ridiculous.
M14 20 shots, magazine change = You eliminated a horde of zeds but backstepped a lot in order to do this, the horde of zeds push you backwards
SCAR 25 shots, magazine change = You eliminated a horde of zeds AND pushed THEM backwards
And the commando has got his AK loaded and ready to fire another 37 rounds if the zeds are not pushed backwards.
Oh, if you guys still don't believe what i was saying, get a HOE bedlam and camp on the L-shaped corridor long road. Walk to the front and guard the debris breach on your right. A commando with a SCAR is (sometimes) able to take out every zed that spawns inside it without the need to retreat. With a M14 SS? Never think of it. Also, even if pushed backwards, the commando need much less space than a SS to handle all of them.