Magazine based reloading. Shoot 3 out of 30 rounds in a mag, drop the old mag, slap a new mag in, you're down 27 bullets and have 30 fresh bullets to shoot, plus one in the chamber.
I used to do this years ago, and its mostly fixed to the point its broken again. 5/30 bullet in my machine gun? No reloading because enemy's at the corner.
In some games they do save the magazines but it isn't common. You'll cycle through all the full ones and go back to ones you've touched, using ones with more and more ammo until you've got none left. I know I was playin a game recently with that in it but I can't tell you for the life of me what it was.
As for Helldivers 2, good luck Diver! Spread that managed democracy like butter. By the way, by now you may have found out that the Termainds are the source of the fuel that Super Earth needs for its FTL tech. That fuel is called Element 710. Turn that upside down lol
And if you ever wanna play Helldivers or something, lemme know! I'd be more than down to play.
Talking about reload mechanics, I think Tarkov has a pretty cool one that wouldn't work for a lot of FPS but is a nice touch for that game. Basically pressing reload takes the mag out, puts it back in your pocket with whatever ammo you had left in it so you can reuse it later, or you can double tap reload to drop the mag on the ground and reload just a little bit faster. I've got plenty of problems with Tarkov, but I did always find that to be a neat touch.