No, marines do not make their own actions. They call Remington, and tell them to send them over. For the shooting team stuff, they may stick 'em in a lathe and blueprint them.
Here's what I'd do for a - new- precision rifle (non-benchrest).
One of Jerry Stiller's Predator actions (a copy of Remington 700, with better precision). .473 boltface, small firing pin.
Shilen Select Match barrel, in either 6mm or 6.5mm.
Jewell or Shilen trigger.
McMillan stock (of your choice).
Leupold QRW rings and bases.
Leupold Vari-whatever 4-14 scope.
I'd get Tom Meredith to do the stockwork (inletting, bedding, etc.) and Billy Stevens to chamber it, probably in 6/284 or 6.5/284, depending on which barrel I got.