Guns and “firearms” are technically two one of a kind things, even though backyard of the army and even in most devices in the military. You can nearly simply get away with the usage of the former phrase to refer to the latter. Both use chemical reactions to propel a projectile thru a tube and then to a target. The distinction is size. A “gun” is a direct-fire crew-served weapon that is too massive for an person to function.
The most frequent weapons in present day navy use are tank cannons and autocannons. Guns are ordnance, that means that they cannot be operated by way of one individual alone, whilst firearms are small arms. Which means that they can be operated via one man or woman alone.