Context: The ammunition and shells fired by these weapons are usually fitted with different types of fuses (barometric, time-delay, or proximity) to explode close to the airborne target, releasing a shower of fast metal fragments. For shorter-range work, a lighter weapon with a higher rate of fire is required, to increase a hit probability on a fast airborne target. Weapons between 20 mm and 40 mm caliber have been widely used in this role. Smaller weapons, typically .50 caliber or even 8 mm rifle caliber guns have been used in the smallest mounts.

Question: What are two types of fuses used for shells?
Answer: barometric, time-delay, or proximity

Question: At shorter ranges a light weapon with what is used on fast targets?
Answer: a higher rate of fire

Question: What size of weapon calibers are better hitting at short range fast targets?
Answer: between 20 mm and 40 mm caliber

Question: Smaller .50 caliber and 8 millimeter guns have been used in what?
Answer: smallest mounts