Of course you know it's a Trick question....
The short bullet in the Left is a 55g bullet 5.56 caliber.
The LONG bullet on the Right weighs 50 g.
I know some of you "smart people" have it figured out. "The Skruske" said the long one was probably Sintered metal which is not Lead core.
I sawed one in half with a hack saw.
Indeed the center of the bullet seems to be some sort of copper powder bonded with something. When you scratch it, it appears copper colored inside.
The German Army used bullets like this in their Strurmgewehr 44 the first Assault Rifle ever. Damsoviets never "Invented" the AK 47....they just made a few changes to the Stg 44.... they always copied everything or stole the technology to make whatever they chose.
This is a photo of a WW2 era box containing ammo for the Stg 44.
The long bullet in question is from the company AmericanReloading.com and they function perfectly well in an AR 15.
Accuracy test later, I got busy on a fence and never got any more loaded.