I know it's not a big thing, but I'm blaming this post on my OCD. LOL!
Not sure if this is a bug or intended but there is a bullet difference between when your character auto-reloads versus when you manually reload; for a mag that should hold 61 rounds, when your character auto-reloads there is only 60 rounds in the mag versus when you manually reload there is the full 61.
This is not a bug, it is actually attention to detail, if you ever fire a real gun until the magazine is empty then change the mag you would have in this case 60 rounds. If you fired your weapon but changed the mag while you still had 13 rounds left you have 12 rounds in the magazine and 1 in the chamber so when removing the magazine you remove 12 but still have 1 in the chamber so adding a mag consisting of 60 rounds actually gives you 60+1.