Well, there's something those 9 or more posts that mentioned/focused on weight repeatedly (Exoskeletons, wheelbarrow comments, etc) have missed.
What's the IAR weigh. What's the SAW it's replacing weigh.
There's about a 10 pound difference to the better for a Marine with an M27.
What's 22 mags weigh empty?
5.5 pounds.
So you're already about 5 pounds lighter out the gate on empty weight to empty weight with about the same combat load. Yeah, 22 mags is going to be janky. Even jankier if you pulled the string to use bandoliers for carrying (I would love to see someone with 22 mags in bandoliers, talk about sloppy the junk wagon... WHERESYOURFRESHMAG I think this might be one no this one wait wtf why am I being strangled)
6 dual mag pouches on a chest rig or whatever you're wearing plus some more on the ruck still won't weigh the same as what a SAW gunner's weapon and associated kit weight was. Spare barrels, anyone?
Everyone isn't mungo in the military like I was and I've come to realize that, but my usual SAW load was 800-1000 and I maneuvered faster than the rest of the squad save my TL who was around 30 secs faster in the 2 mile than me and was irritated that he plateued around 11:15 in that regard. If someone gets bitchmade by carrying a weapon system and it's associated equipment, either they need to train more (and harder) or they need to be swapped out to a duty position their intestinal fortitude can accomodate.