MARINE CORPS BASE QUANTICO, Va. — It's official — the M4 carbine has replaced the M16A4 as the universal rifle of Marine Corps infantry.

Commandant Gen. Robert Neller has signed off on the switch making the M4 the primary weapon for all infantry battalions, security forces and supporting schools no later than the end of September 2016, according to an internal memo released by Lt. Gen. Ronald Bailey, deputy commandant for Plans, Policies and Operations via the Automated Message Handling System.

The recommendation was first made over the summer to then-commandant Gen. Joseph Dunford, and its final approval was one of Gen. Neller's first orders of business after succeeding Dunford Sep. 24, according to Marine Corps officials.

"We made the proposal, and we just got the head nod from the commandant," said Chris Woodburn, a retired lieutenant colonel who now serves as the deputy Maneuver Branch head for the Manuever Branch deputy, Fires and Maneuver Integration Division of , Capabilities Development Directorate, Marine Corps Combat Development Command. "We get improved capability at no cost,: a smaller and more compact rifle that shoots better for infantry."

As a shorter OK??/km leaner rifle than the M16A4, the formal adoption of the M4 means increased capability and mobility across the force as the Corps looks to modernize in a resource-constrained environment.

Gen. Neller's decision The switch comes after extensive testing — and combat experience — demonstrated the M4 outperformed the M16A4 across the board, according to Marine Corps officials.

"We found out that the M4 actually outshoots the A4 at all ranges out to 600 meters with the new ammunition," Woodburn said, referring to the 5.56mm AB49 Special Operations Science and Technology cartridge the Corps is looking to make the standard.

At least half the force already has the M4s as a personal weapon already, which means that the conversion will come at no cost to American taxpayers, save that of transporting the rifles.

The redistribution, Woodburn said, will occur in two phases.

First, each of the Marine expeditionary forces will redistribute M4s across their armories and ship excess rifles to Marine Corps Logistics Command, along with their rifle combat optics.

Any unit which is short M4s per its table of organization and equipment will then apply to LOGCOM to make up the difference.

"It's important to emphasize that no one who rates an M4 by TO is going to lose an M4," Woodburn said. "These are excess M4s that are already in units, and we have an amount at LOGCOM already."

The goal, Woodburn said, is to have the first phase complete by the end of third quarter of fiscal year 2016, and the total redistribution accomplished by the end of the fiscal year.

Exceptions, he noted, will be for those units either getting ready to deploy or returning from deployment.