Barrel twist rate?
Interesting, few of these reports seem to be coming from troops 20" or SAW platforms. It would seem that the additional velocity from the longer barrel provides adequate usable fragmentation range for M855 in the majority of cases. From shorter barrels, such as the M4's 14.5" barrel, M855's fragmentation range varies from as much as 90m to as little as 10m, which frequently isn't enough range.
I suggest you NOT try the 75 gr A-Max.It just won't work loaded to magazine length.