Excaliber's question is a good one. Could I suggest a reply that cites at least one of the following advantages? :
1- Higher ballistic coefficient through improved form factor.
2- Higher inherent accuracy attributable to manufacture tolerances.
3- Higher potential muzzle velocities consequent to structural rigidity.
4- Lower throat heat-erosion consequent to smaller coefficient of friction.
5- Lower cost for equivalent performance.
6- Compatibility with existing magazines without reduced propellant capacity.
Since the Berger has you on mass, and the 300 grain CE requires a twist-rate less than 1: 9" (the tightest twist commonly mounted), it is likely that the 278 grain MTAC has an advantage in #2, and possibly #3, and #4.
To establish this you would need to compare groupings, and record maximum muzzle velocities.
