OK, I've seen the very occasional primer ejection with arsenal loaded US ammo. I agree you might have picked up a couple overused empties. That said:

1. Do you have a case gauge? If not, get one and verify the headspace adjustment of your dies. DO NOT accept the idea that if you set factory dies per factory instructions, you'll have proper headspace on your loaded rounds. Do watch overall length, I generally load to 2.240-2.250 for ball equivilent.

2. Are you trimming brass? If not, better start. It affects #3.

3. Are you crimping your bullets? If not START NOW! The AR system is hard on ammo in the loading cycle. The carbine length gas system is downright violent. Bullet setback during the feed cycle raises pressures much faster & higher than bullets in the rifling per independent testing.

4. Powder choice & charge weight. As noted by other above, you're at max, leaving no room for variables. Change powder to something more appropriate for the case and back off a grain or so. Somewhere around 2900 f/s is good for 55 gr bullets in a 16" barrel. Around 21-22 grains of either 4198 will do that and save you money in the long run.

I know a couple guys who load certain powders in .223 because they only want to stock one rifle powder. They end up with loads that certainly aren't optimal for the platform/caliber. Depending upon what bullet I'm loading I may use one of 4 powders.

5. Being over enthusiastic in primer pocket crimp removal can result in loose primer pockets. When I pick up any used 5.56 mm empties, if they aren't bright brass cases with the primers still crimped in, they go in the range trash barrel.

Slight detour- I've never tried the bullets you're using. I stick with standard jacketed bullets in large part because of the violence of the feed cycle of the AR/carbine system [it's been demonstrated to occasionally destroy frangible-compressed & bonded copper powder- bullets, leading to the development of that type of core being inserted in a normal jacket for similar results on steel targets without the problems]. I have no clue if that might affect anything, but I'm not willing to experiment with my own gear.

Sorry if I'm beating basics to death, but loading for semis isn't the same thing as loading for your bolt guns.