What is one characteristic of the M4A1 carbine?

The M4A1 carbine's characteristic of being a magazine-fed weapon indicates that it utilizes detachable magazines to hold ammunition, allowing for quicker reloads and ease of use in combat situations. This design is integral to modern firearms, particularly in military applications, as it enhances operational efficiency and adaptability in various combat scenarios.

The other options do not accurately describe the M4A1. It is not a multi-shot revolver, which typically relies on a rotating cylinder mechanism. It is also not a shotgun, which is designed for firing multiple projectiles simultaneously, nor is it classified as a sniper rifle, which is built for long-range precision shooting. The classification of the M4A1 as a magazine-fed carbine underscores its versatility and tactical relevance for infantry use.