The AR-15 can be either a carbine or a rifle depending on barrel length and overall configuration. The term "carbine" refers to a short-barreled rifle, typically with a barrel under 16 inches, and the AR-15 platform accommodates both configurations. Most common AR-15s use 16-inch barrels, which technically classifies them as rifles rather than carbines under federal definitions. However, AR-15 carbine variants with shorter barrels (10.5 to 14.5 inches) are manufactured and sold, along with legal short-barrel rifle (SBR) versions requiring special registration in jurisdictions where permitted. The AR-15 platform's modular design makes it flexible—shooters can configure the same lower receiver with different upper assemblies to create either a rifle or carbine setup. When discussing AR-15s generically without specifying barrel length, "AR-15" usually refers to the standard 16-inch rifle configuration rather than the carbine variant, though the distinction matters for legal compliance and practical purposes. The distinction between AR-15 rifles and carbines primarily affects handling characteristics, ballistics, and legal classifications, but both use the same basic operating system and magazine compatibility.