A single barrel externally powered gun includes a feed mechanism, a bolt assembly, a bolt control assembly and a power transmission system. The bolt control assembly is in the form of a chain drive unit driven continuously along a predetermined path of travel which defines the timing and sequence of loading, ramming, firing and ejecting. The chain drive assembly controls the reciprocating motion of the bolt assembly relative to a fixed non-rotating and non-reciprocating barrel, the bolt being stationary in the firing and loading sequences. The feed mechanism which continuously advances rounds is integrated to the intermittent motion of the bolt by a Geneva wheel mechanism, as the bolt assembly reaches the proper position in its rearward movement. Bolt locking, firing and unlocking are all controlled, and carried on while the chain drive assembly is continuously moving. In another form, a parallel index drive assembly may be used in place of a Geneva wheel mechanism with resultant simplification of the overall gun structure. A power transmission system operates to effect synchronous movement of the feed and bolt control assemblies. Rates of fire of between 500 and 1000 rounds for a single barrel weapon are possible, with increased total rates if multiple barrel guns are provided.