poison gas while firing my AR rapidly

[masakari]

So I noticed that when I fire 3 to 5 shots rapidly though my AR at the local indoor range, I get gassed pretty badly. It is an unpleasant feeling and makes me wince. Now im pretty used to it, and its happened many times before, but I feel like its a bit much out of my M4, and i dont remember ever experienciing it in any of my issued weapons, aleit most of those were fired outside. It is a CMMG upper on a Spikes lower, with a BCM gunfighter charging handle. Is it normal for it to be so prominent? Take note, I shoot VERY quickly during these strings.
heres the rifle in question:


Thanks guys