I know what these are because I made ones just like these myself in machine shop. They are a copy of a 50 BMG bullet turned from solid steel on a lathe. Most likely a CNC lathe because those curves and radius is are almost impossible to do by hand. The exercise involved accurately measuring all dimensions of an actual 50 caliber BMG bullet and then translating that into numerical code.Once my program had run , I cut the bottom piece off. The part that has been left on the bottom of the bullet is what the lathe chuck holds on to. The ones you have are basically a novelty or ornamental bookends perhaps since I completed by bullets and they were very accurate I could actually use them to check the accuracy of a chamber of a gun yours however will not go into a gun with the bottom piece of metal still attached.

I know what these are because I made ones just like these myself in machine shop. They are a copy of a 50 BMG bullet turned from solid steel on a lathe. Most likely a CNC lathe because those curves and radius is are almost impossible to do by hand. The exercise involved accurately measuring all dimensions of an actual 50 caliber BMG bullet and then translating that into numerical code.Once my program had run , I cut the bottom piece off. The part that has been left on the bottom of the bullet is what the lathe chuck holds on to. The ones you have are basically a novelty or ornamental bookends perhaps since I completed by bullets and they were very accurate I could actually use them to check the accuracy of a chamber of a gun yours however will not go into a gun with the bottom piece of metal still attached.

References:

I was not able to find a reference anywhere of someone who actually made a 50 caliber bullet on a CNC lathe except for myself