This has been done for years, it's nothing new so to speak. The guy is clear that he's either at the CP which is close by or at the rear with a support element, not in a direct action role. Give the guy a break.
OP, What caliber are they using? As advised, pick up a factory upper, 11.5" if 5.56 and look into a suppressor. I would think if they permit you to carry a "long gun" that they would issue it. If not, what are they using and post that. Have a means of securing it as you render aid. Would imagine some training consist of a downed member and have the rifle with you to see how to secure it on your body so not to hit and or flag others. Another point of view is you would be purely defensive with the firearm and if required to render aid, you would have available that members firearm to use if the need arose. At least they should have you be familiar with and train with the issued long gun. I don't know your skill level, but know how to manipulate it, deploy it, clear malfunctions and clear/safe it. Most likely you would be clearing the team members gun or at least securing it.
In my opinion if one or a team is doing this line of work, train up has been done to prep for house work. "CQB" really shows strengths or weakness in one's ability to manipulate a firearm. There are drills to accomplish this, you would be surprised of the lack of muzzle control in these environments.