A carriage (240, 240', 340) for use with a surgical guide, comprising: a housing (250, 250', 350) having: a proximal end (250p, 250p', 350p); a distal end (250d, 250d', 350d) opposed to the proximal end; opposed first and second side surfaces (250r, 250s, 250r', 250s', 350r, 350s) extending between the proximal and distal ends; and opposed first and second facial surfaces (250f, 250g, 250f, 250g', 350f, 350g) extending between the proximal and distal ends and the first and second side surfaces; a guide-receiving opening (244, 344) extending through the housing and through the first and second side surfaces, the guide-receiving opening being configured to receive an arm of a surgical guide along which the carriage is configured to translate; and a bullet-receiving opening (242, 242', 342) extending through the housing and through the proximal and distal ends, the bullet-receiving opening being configured to be open towards the first facial surface to receive a bullet (270, 470) for use with a surgical guide associated with the carriage, and wherein the bullet-receiving opening is configured to hold a received bullet in a locked position in which said received bullet cannot translate between the two side surfaces or between the two facial surfaces; characterized in that the bullet-receiving opening is configured to receive a bullet (270, 470) by passing the bullet from an outside environment, through the first facial surface, and into the bullet-receiving opening. a housing (250, 250', 350) having: a proximal end (250p, 250p', 350p); a distal end (250d, 250d', 350d) opposed to the proximal end; opposed first and second side surfaces (250r, 250s, 250r', 250s', 350r, 350s) extending between the proximal and distal ends; and opposed first and second facial surfaces (250f, 250g, 250f, 250g', 350f, 350g) extending between the proximal and distal ends and the first and second side surfaces; a proximal end (250p, 250p', 350p); a distal end (250d, 250d', 350d) opposed to the proximal end; opposed first and second side surfaces (250r, 250s, 250r', 250s', 350r, 350s) extending between the proximal and distal ends; and opposed first and second facial surfaces (250f, 250g, 250f, 250g', 350f, 350g) extending between the proximal and distal ends and the first and second side surfaces; a guide-receiving opening (244, 344) extending through the housing and through the first and second side surfaces, the guide-receiving opening being configured to receive an arm of a surgical guide along which the carriage is configured to translate; and a bullet-receiving opening (242, 242', 342) extending through the housing and through the proximal and distal ends, the bullet-receiving opening being configured to be open towards the first facial surface to receive a bullet (270, 470) for use with a surgical guide associated with the carriage, and wherein the bullet-receiving opening is configured to hold a received bullet in a locked position in which said received bullet cannot translate between the two side surfaces or between the two facial surfaces; characterized in that the bullet-receiving opening is configured to receive a bullet (270, 470) by passing the bullet from an outside environment, through the first facial surface, and into the bullet-receiving opening.