The 75% standard is still the 308. Marines still use a short action 700 and the Army has a long action 700 M24 that they are eventually replacing with the new XM2010.
You have some using the 300 Win (SEALS, other SOF) and the Army just bought 3600 of the new XM2010 Remingtons (MSR) in 300 Win Mag. MSR can change calibers, but right now only the 300 has been purchased and approved.
Another 10% (SOF primarily) using the 338, though testing the 338 packages for conventional forces along with SOCOM (AI and Remington MSR).
then you have the 50 in the Barrett in quite a bit of use in specialty situations.
UPDATE: Just confirmed that the SOCOM 338 bid is in dissaray right now. All failed the 1500m accuracy shoot. No details why, but that puts the bid into a stop and now they will have to resolicit, so no one has the 338 as an official sniper rifle yet.
BH