On the topic of bullet calibers

[Hazeron]

Can someone explain to me what the hell happened to bullet measuring in the years leading up to the apocalypse? 9mm is somehow more powerful than 7.62 (which is a rifle grade round), 7.62 is apparently now a pistol and SMG caliber, and everyone started calling .50 BMG 12.7mm.

[xammurapi]

9mm is somehow more powerful than 7.62 (which is a rifle grade round), 7.62 is apparently now a pistol and SMG caliber,

7.62 in this game looks very similar to https://en.wikipedia.org/wiki/7.63%C3%9725mm_Mauser

[Hazeron]

Ah.

[Davinrarre]

Since the developers of this game are mainly Eastern European, they were probably partly influenced by Russian and European weapons/ammunition when they made this game.  There are several references to Russian/Eastern European weapons in the game that Americans may not recognize, but are in fact very iconic to the developers (TT3000 a reference to the Tokarev TT-33, ZC99 a reference to the Zastava CZ99, the Dragunov, and the Black Arrow being a reference to the Zastava M93 Black Arrow).  Thus the 12.7mm round is probably in reference to the Soviet 12.7mm (https://en.wikipedia.org/wiki/12.7%C3%97108mm) rather than the .50 BMG, and the 9mm in-game might be a reference to the Russian 9x39mm (https://en.wikipedia.org/wiki/9%C3%9739mm).

[Sanger]

Eastern European handguns also use a 9mm round. But I don't think the ammunition in this game is really meant to make sense. There's no explanation for why the same rounds can fit into a handgun/submachine gun or rifle magazine (though the two have distinct lengths, as seen in the graphics for their extended magazine upgrades) -  the game simply doesn't focus too heavily on gun stuff and the developer probably just didn't want to bog it down with too many different ammunition types.

[ShadowRun]

I know plenty of Fallout -inspired games have a vast array of numeric ammunition, but to someone who has never been in the military, it's all pretty baffling. To me, there are just bullets, arrows and bolts. Mysterious numbers that refuse to work with the currently selected weapon make me equip a less fussy weapon. (I'm playing a psion, wielding a jackknife.)

[Sanger]

It's not difficult. I've never been in the military and have little personal interest in guns, but I understand the idea behind how they work. A gun cartridge is a bullet attached to a case full of gunpowder. Long cases contain more gunpowder. Short cases container less gunpowder. For a handgun you want a bullet without too much power behind it so that it doesn't fly out of your hand when you shoot it. For a rifle you can use a bullet with much more power behind it. So rifle bullets have long cases and are more powerful, pistol bullets have short cases and are less powerful.

Their magazines reflect this. Pistol magazines usually go in the grip, so if you tried to put rifle rounds in a pistol, you'd end up with something like this: