An apparatus, system, and method are provided for injecting carrier sleeves into a wellbore. The injection system is capable of individually indexing a selected sleeve from a sleeve magazine into an injector bore and axially aligning the sleeve with the bore with a retaining device. The retaining device prevents a subsequent sleeve from being indexed into the bore from the magazine. The selected sleeve can be restricted from free fall using a staging mechanism, which can subsequently be opened to permit the selected sleeve to fall into a staging bore. The staging bore is then fluidly isolated from the injector bore and the wellbore, pressure in the staging bore is equalized with the wellbore, and then opened to the wellbore for injecting the sleeve into the wellbore. The sleeve can be axially aligned and radially centered with the injector bore using a tapered portion in the bore or the staging mechanism.