In Soviet Rus...uh, Eastern USA, wait...

[Mark W.]

It's an M1 Garand in proper military condition the so called third sling loop on the muzzle end of the rifle is the stacking swivel. Used to interlock with the same on two other rifles to create a tripod of rifles to keep them up out of the mud. Same method has been used since at least the Civil War.

 

[salmonriverjohn]

Thank you Mark W, I learned something new today!