I do not know about 277 USA but I believe 277 Wolverine is 223 based - similar to 300 BO but with a 6.8 projectile. You see it discussed on the 6.8 Forum. I have 6.8 SPC and 6.5G AR uppers so I spend time on those forums. 9 vs 45 discussions are nothing compared to 6.5G vs 6.8SPC "discussions".