A machine gun fires more than 1 rifle caliber round each time the trigger is pulled. A sub-machine gun fires more than 1 pistol caliber round each time the trigger is pulled.

Machine guns are more common among long range battle engagements due to the longer effective range of rifle caliber rounds. Sub-machine guns are often employed for close quarter battle (CQB) where the use of short-barreled weapons is desired.

These are popular rifle calibers for machine guns:

• .223/5.56 - AR-15, HK 416, FN SCAR
• 7.62x39 - AK-47
• 7.62x51 - HK 91, FN FAL
• 5.45x49 - AK-74
• .300 Blackout - AR-15

These are popular pistol calibers for sub-machine guns:

• 9mm - MP5, UZI
• .45 ACP - UZI, HK UMP
• 5.7x28 - FN P90, AR-15
• 4.6×30 - HK MP7

Read more about machine gun ownership.