Range Report .223 Rem in MK262 5.56 Chamber

[rideHPD]

I'm sure this question has been rehashed to death, but with the new search engine I can't find a direct answer; is anyone finding that factory match .223 Rem is underperforming in rifles with the MK262 chamber? I ask this because I know the NATO chamber should have a longer throat and I'm not sure if (FGMM) 77gr .223 Rem has a shorter COAL than the MK262, and don't have a set of calipers handy to test this.

 

[Alaska]

No difference in throat until you get to above 77gr as stated in the Sierra Reloading manual.

The shorter COAL for the MK 262 is to prevent bullet run out by Black Hills.

2.245"