Help identifying this ammo

[Wellsdw]

An older gentleman stopped by the hardware store I was working at and asked if anyone new anything about These rounds. Only thing I could say , was it looked like a 308 with a different “back”.
Also he took it with him so I can’t get another look.

Thanks for any insight

 

[Wyobohunter]

Looks like 7.62×54mmR to me. Old Russian military ammo.