Norinco M4 question

[RACKMAN]

I'm new to black rifles so this may be a question because I've missed something obvious...I've just ordered a Norinco CQB-M4 and as I've been reading through Norinco M4 threads I've noticed that there is CQA and CQB designations...what is the difference between CQA and CQB M4s? Thanks.

RACKMAN,

 

[enefgee]

CQ-A556 = Norinco Model # CQB- what you would use an M4 for (military term: Close Quarters Battle)