Doctrine and why the Grendel has an uphill battle.

[LRRPF52]

I just weighed a 25rd Grendel magazine with 25 Federal 120gr HPBT Match Load cartridges on it. Came to 1lb 5.4oz / .60kg
30rd Magpul PMAG with 69gr SMK HPBT load is 1lb 2oz /.51kg

7 x 30rd .223 Rem 69gr = 3.57kg or 7.87lbs for 210rds
7 x 25rd 6.5 Grendel 120gr = 4.2kg or 9.2lbs for 175rds

Body armor takes up 10-16lbs for just the plates and carrier in a SOF unit that doesn't mandate soft armor, so that is the 500lb gorilla in the room that has changed with soldier's load, and very little has been done to progress hard plate technology past Vietnam-era aviator's ceramic armor plates. Regular units are saddled with IOTV, which is even more weight to consider.

As far as mags go, it changed everything from where we were able to carry double M4 pouches comfortably across the chest, to now where single shingles are really the only practical way to be able to stay as low-profile as possible. Negotiating in and out of vehicles, window frames, breech points, tight confines, climbing walls, ladders, and rubble present serious challenges even for units with PT standards that crush the regular Army lacking standards of physical fitness.

This is why I quickly started to see the 6.5 Grendel as something that should be replacing 7.62 NATO, not 5.56 NATO. A 6.5 Grendel/5.56 NATO weapons mix would be a breath of fresh air for Joe, who is laden with a lot of squeeze for little juice with 7.62 NATO. We need to get the 5.56 NATO systems weighing less, like the originals, but with Electro-Optical Aiming and Vis/Non-Vis Illumination capability.

6.5 Grendel DMR/CSASS/LMG makes a lot of sense.
Smaller 5.56 carbines
That Colt MARS or the KAC PDW would be great really for a lot of people.