There's...
Which aircraft? In WWII armament ranged from zero (trainers, etc) to rifle-calibre machine guns, heavy machine guns, cannons (15 mm upwards), heavy guns (57 mm, 75 mm, 105 mm), rockets, torpedoes, bombs, mines...
The Mitsubishi A6M Zero had two 20 mm cannon and two 7.7 mm (.303 in) machine guns .
Basically, airsoft guns are built to fire plastic 6 mm BBs. Even though several manufacturers recently pack CO2 magazine in their GBB (i.e. KJW), it still means to fire 6 mm plastic BBs. Airsoft gun with CO2 mags can fire metal BBs or glass BBs, but those kinds of BB will decrease the age of the inner barrel. You need to upgrade the inner barrel to fire metal or glass BBs.
A "155" artillery round is a 155 mm (diameter) shell, approximately 6 inches. Examples of guns that fire this type of shell are the 155 mm M114 howitzer, developed just before World War II.
There are various types of ammunition. There are also particular guns that use the recently developed 30 mm ammunition. Among them are aircraft guns and armoured vehicle guns.
Size of the bullet
Both the interceptor and fighter-bomber versions of the F-86 Sabre carried six 12.7 mm M3 Browning Machine Guns
7.62 mm (or 30 caliber) and 5.56 mm (or 223 caliber) are common rifle cartridges. Pistols, machine guns, and artillery will of course be different from these.
No, It says to use them only in low powered spring guns. They will probably explode if used in an AEG.
They've been found to be more effective than the previous 9mm guns issued.
Possibly 40 mm. After the war, 40 mm then later 75 mm.
The kindle fire is 7.5 inches by 4.7 inches.