57-N-231 standard 7.62×39mm military bullets with steel core - the one on the left is unfired, the one on the right is fired, with the rifling grooves visible. Notice the copper wash scraped off and the steel jacket is exposed on the groove marks.
<a href="//commons.wikimedia.org/w/index.php?title=User:Vic2015&amp;action=edit&amp;redlink=1" class="new" title="User:Vic2015 (page does not exist)">Vic2015</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>