He is writing a letter.

He waved his hand.

An electron gun is a device for generating an electron beam.

He is known as a French musketeer.

He shot the enemy with a machine gun.

He went to try out his new air gun.

He headed to the battlefield with an assault rifle.

He was handling the carbine carefully.

He defeated the enemy using a sniper rifle.

The police used a water cannon against the demonstrators.