By Jennifer BacchusNovember 15, 2018
ANNISTON ARMY DEPOT, Ala. -- The depot, once again, lived up to its reputation as the Pitcrew of the American Warfighter as it quickly responded to a need to modify M4/M4A1 main selector levers on-site.
"An unintended discharge/failure to fire issue arose when the selector was placed in a position between SEMI and AUTO. This position is outside of a proper detent position, however when the trigger is pulled, with the selector in this position, the weapon should fire. This failure to fire event happened when the trigger was pulled, but weapon did not fire," said Anthony Cautero, assistant program manager for U.S. Army Program Executive Officer Soldier.
The ambidextrous main selector lever met specifications, which required the part to have a 90-degree angle.
"An investigation discovered that, under certain circumstances, interference between mating parts caused the weapon to fail to fire. Then, further rotating the lever led to an unintended discharge," said Cautero.
The issue affected approximately six to nine percent of all M4s in service in the Army.
Following that investigation, the U.S. Army Tank-automotive and Armaments Command, ANAD's higher headquarters, took the lead on improving the process to modify the lever.
While working to create a fix for the affected M4A1 weapons, the command sent two safety of use messages, instructing Soldiers to continue following proper firing procedures, perform additional function checks and confirm the selector is in a detent position before performing immediate action procedures.
The U.S. Army Armament Research, Development and Engineering Center coordinated with the original equipment manufacturer, Colt, to supply a sample quantity of selector levers with a 45-degree angle to test.
In July, PEO Soldier and ARDEC sent information and modification equipment to ANAD, along with trainers, to make the modifications by hand.
For the employees of the depot's Small Arms Repair Facility, this was an unusual set of circumstances.
"In our business, we don't usually modify parts. Either they are good or bad. Either they meet specifications or not," said Paul Barber, chief of ANAD's Weapons Division. "These parts met the original specifications, but required modification to meet new specs and ANAD was in a position to perform that modification process."
ARDEC and PEO Soldier personnel brought 24 fixtures and files with them to assist with the modification work. Ten employees were assigned to cut a 45-degree angle into the selector levers, by hand, using the fixtures and the files provided.
On the first day, they produced 200 levers.
Barber quickly realized the depot would not be able to fulfill the request of 22,000 levers by the beginning of September and began to research other methods. He turned to Steve Pennington, the deputy director of Production for the Component Repair and Weapons Value Stream, and they put together a team of experienced machinists from throughout the installation.
Lance Jennings was one of the machinists recruited to look at the problem.
With 36 years of experience, he knew the process could be done quicker and more accurately on a computer numerical controlled milling machine.
"You can't beat the repeatability of the CNC machine by hand," said Jennings.
The CNC machine was quickly programmed to work with the fixtures from ARDEC. Using those fixtures, Jennings found he could modify three levers at a time. But, he knew a more efficient fixture could be developed.
"We came up with an idea to place the levers in a fixture on a one-inch center," said Jennings, explaining there was one inch between the center of each lever in the fixture, enabling seven levers to be milled at the same time.
The fixture was designed to work with a standard CNC milling machine vise and soon the fixtures were running on four machines in three shops - one in Small Arms, one in the Manufacturing Division and two in the Powertrain Flexible Maintenance Facility.
Two of the machines, operating with two employees, could modify about 200 levers per hour - a dramatic difference from the 10 employees needed to modify 200 levers in nine hours.
And the CNC-milled levers were more accurate to specification than those which were hand-filed.
"With hand filing, how accurate can you be? With the CNC machine, it is accurate every time," said Pennington.
ARDEC performed 100 percent inspections during the first two days the levers were modified using the CNC machines. Finding no defects, they approved the process with spot inspections.
With the new process in place, the depot was on track to meet its Sept. 1 deadline to modify 22,000 levers.
"Not only did we meet the deadline, we completed it ahead of schedule," said Barber.
Because the levers are part of a weapon and were being modified at shops not collocated with the Small Arms Repair Facility, accountability for every part was vital. Inventories were performed before the levers left Small Arms, when they arrived at the other facilities, when they left that facility and when they arrived back at Small Arms.
"This selector lever issue illustrates what our depots and arsenals do for Army readiness," said Maj. Gen. Daniel Mitchell, TACOM commanding general. "They solve near term readiness issues and are ready to surge in case of war."
Now that the first 22,000 selector levers have been modified, the process will move toward replacing levers in the affected M4A1 weapons throughout the Army. This may require the use of some of ANAD's traveling teams of small arms repairers, a decision which must be made by TACOM.
Only 100 levers were scrapped during the CNC milling process, according to Barber. Of those, only a small portion were from the milling process itself. The rest were non-conforming parts, which wouldn't fit the fixture.