Anything belt fed will hold the most, most belts being around 200 rounds. More can be added to the end of the belt however so its really limitless. If your asking about something with a clip (not a drum, a clip) I'd guess FN P-90's are close with 50. Prolly could go Google that though.
Japanese
It depends there are many different .308 guns.
Most modern guns DO fire bullets that break the sound barrier. That is, their bullets travel faster than the speed of sound when they are fired.
yes they are. machine guns are fed bullets. Gatling guns are hand cranked and have to be fed bullets at the same time. machine guns also spray bullets faster than Gatling guns.
air and gun powder are the most common.
Assuming you mean "machine guns," when most people use the term, they mean a gun that is fully automatic. That means you can hold the trigger down on the gun and it will continuously cycle the action and fire the bullets that go into the chamber.
Yes, guns shoot bullets
Most flare guns are single shot.
Yes, machine guns are much faster than Gatling guns. Gatling guns must be hand cranked and fed bullets at the same but machine guns does not have to be hand cranked. All they needs are bullets. Machine guns also fire more bullets faster than Gatling guns.
guns that kill you with bullets
First, in options, their are a number of "cheats". If you click slow bullets, hence the name, the bullets will slow down (default). Also you can turn on the Cheat: All Guns Available bullets to use all guns in the game. Have Fun! You can hold ztl for minigun and hold xhi for rocket lancher i don't know the code for super shotgun use these cheat codes in battle.
In most US states there is no restriction on who can buy ammunition, just sometimes on the amount. The major restrictions are on the guns that fire the bullets.