The 7.62×51mm NATO is a rimless, bottlenecked rifle cartridge. It is a standard for small arms among NATO countries.

First developed in the 1950s, the cartridge had first been introduced in U.S. service for the M14 rifle and M60 machine gun. Many other firearms that use the 7.62×51mm NATO remain in service today, especially various designated marksman rifles/sniper rifles and medium machine guns/general-purpose machine guns (i.e. M24 Sniper Rifle and M240 Medium Machine Gun). The cartridge is used by military personnel, on mounted and crew-served weapons that are mounted to vehicles, aircraft, and ships.

During my time with the Bundeswehr, we shot them in both the famous G3 and MG3.

This caliber is quite similar to the .308 Winchester, which is a civil version. Although it is technically possible, it is not recommended to swap them out.

I modelled this in SolidWorks according to a drawing from Wikipedia:
https://en.wikipedia.org/wiki/7.62%C3%9751mm_NATO

When importing the 3mf-File into prusa slicer you will be asked if you want to join the pieces together. Answer NO and you will be able to print them out separately.