The concern is level IV body armor. By definition, it can withstand 30-06 steel-cored AP. To give an idea, one source stated that basic level IV is about 16mm (about 5/8") of RHA (Rolled Homogeneous Armor) plate. The numbers that I have seen indicate that RHA is just a little bit weaker than AR500. Both 6.5 CM and 260 Rem have been tested (the latter by the French Special forces) and they could not penetrate to a great enough distance. My guess is that the goal of defeating level IV at 600m is just too ambitious and will be reduced.
It is important to note that all of the NGSW rifles have some type of recoil mitigation other than suppressors. This of course, makes them more complicated and expensive. The video above mentions that the SIG has roughly the same recoil as a FAL and in another video he mentions that the RM277 that shoots the polymer round has low recoil. https://www.youtube.com/watch?v=BoBOuv6qJNU
So far, the US has not had the problem of opponents wearing modern body armor. That will not last long, and the shit will hit the fan the first time we encounter someone else wearing armor close to our own. 5.56 tungsten cored AP from M4's usually can't get through Level IV, although sometimes rifles with 20" barrels can (at least according to some youtube videos that I have seen). Modern body armor is becoming less expensive. For example, level IV is being worn by both sides on the Syrian conflict, and Syria is not a wealthy country.
edited to add: Level IV spec: 30-06 M2 AP bullet (166 grains) at 2880fps
It is important to note that all of the NGSW rifles have some type of recoil mitigation other than suppressors. This of course, makes them more complicated and expensive. The video above mentions that the SIG has roughly the same recoil as a FAL and in another video he mentions that the RM277 that shoots the polymer round has low recoil. https://www.youtube.com/watch?v=BoBOuv6qJNU
So far, the US has not had the problem of opponents wearing modern body armor. That will not last long, and the shit will hit the fan the first time we encounter someone else wearing armor close to our own. 5.56 tungsten cored AP from M4's usually can't get through Level IV, although sometimes rifles with 20" barrels can (at least according to some youtube videos that I have seen). Modern body armor is becoming less expensive. For example, level IV is being worn by both sides on the Syrian conflict, and Syria is not a wealthy country.
edited to add: Level IV spec: 30-06 M2 AP bullet (166 grains) at 2880fps