A multi-caliber ambidextrously controlled firearm that includes an adjustable ejection system to facilitate the ejection of spent cartridge casings from a firearm. The adjustable ejection system includes an ejection port defined by an aperture in the firearm and a deflector. The deflector is attached to the firearm to adjust the size of the ejection port and may be attached at one of at least two attachment positions of the firearm. The adjustable ejector system includes an ejector selectively attached to the firearm at one of at least two ejector attachment positions. The improved firearm also includes an ambidextrous magazine catch system for selectively retaining a magazine within a firearm. The magazine catch system includes a first button opposite a second button such that either button may be actuated by a user to release the magazine retained with the firearm.