Mar 2, 2011

Picatinny cobalt alloys show promise for sustained firepower

Photo Credit: Jesse Glass.

Far right, engineer Vinny Leto holds one of the various cobalt alloy barrels produced using the flow forming technique. The shortest barrel was the first produced, followed by full length barrels without rifling and later a prototype with rifling like the one that was tested. Other team members, from left, Michael Hespos and Keith Koehler.
PICATINNY ARSENAL, N.J. -- During a firefight, the last thing a machine gunner wants to do is stop fighting to change barrels, but that's how it has always been done with standard, single steel-barrel machine guns.
The reason for the barrel change is that at high temperatures barrels lose "strength properties," according to engineers working on a promising alternative.

One of the engineers is Vinny Leto, systems project engineer, of the Armament Research, Development and Engineering Center, or ARDEC, Weapons System Technology Directorate. During a test firing of a proof-of-concept barrel in December, Leto witnessed a measure of success with the High Performance Alloys for Weapons Applications Project.
During testing, the first rifled, cobalt-alloy machine gun barrel ever produced using the "flow forming" process consistently reached high temperatures without degraded performance.
The proof-of-concept barrel was made of an alloy that contains more than 50 percent of the metal cobalt. Cobalt alloys are erosion- and corrosion-resistant metals that are designed to retain high strength during long-term exposure to high temperatures.

Cobalt alloys are frequently used in the aerospace industry, such as the hot-gas section of turbine engines, explained Leto. Cobalt alloys are also used as short liners for machine gun barrels.
"If you look at steel in a machine gun environment, it gets very hot at a high rate of fire," said Leto. "The benefit of the cobalt alloy is that it is designed to operate in high-temperature, high-stress environments. It has the added benefits of corrosion and erosion resistance."
While cobalt alloy barrel liners have been produced for years, it is very difficult with existing machining techniques to impart rifling. "The material, for all of its phenomenal properties, is very difficult to manufacture and machine," said Leto.

Different from machining, flow-forming is an advanced process used to manufacture precise cylindrical components. The process consists of high-pressure rollers exerting pressure on the exterior of a cylinder, pressing material against a rod-called a mandrel-on the interior of the cylinder. For this project, the flow-forming process was modified to produce the rifling in the barrel bore.
More testing and data gathering will be required before engineers know if flow forming manufacturing can be achieved with the alloy.
Success, however, would provide warfighters with three potential benefits: lightening their load, increasing barrel service life, and giving them a barrel that could operate at higher temperatures compared to a steel barrel, Leto said.

Soldiers and Marines typically carry spare barrels into battle so that they have a cool barrel to exchange if they engage the enemy in a firefight, explained Leto. Having that strength at higher temperatures means that barrels may not need to be changed during a firefight, eliminating the need for the extra barrel and maintaining a steady stream of firepower.
Engineering team members met all of their proof-of-concept test objectives when they fired more than 24,000 rounds and achieved an 1,100 degrees barrel temperature. Leto said the alloy barrel was fired from the ARDEC-designed Advanced Remote/Robotic Armament System.
Steel begins to lose strength at approximately 1,000 degrees, Leto noted, and the test yielded data needed to assess and design the next round of improvements. The team is planning to produce another prototype that will be fired from a fielded infantry weapon later this year.
Previously, the engineers had produced a half-length barrel as an initial demonstration of the flow-forming process before moving on to manufacturing full-length barrels.

The Office of Naval Research assigned the engineers as principal investigators into the flow forming manufacturing technology. They are leveraging ARDEC's expertise with metallurgy and small arms design and analysis. Prototype testing will be conducted here at the Armament Technology Facility, which is ARDEC's small arms design and evaluation facility.
Previously, the engineers had worked with the Office of Naval Research in development of lightweight 60mm and 81mm mortar tubes made with a nickel-based alloy.
The team is also working with the Joint Services Small Arms Program, which is also based at Picatinny Arsenal. The JSSAP office oversees the day-to-day implementation of the plan by the joint services regarding the development and investment in small-arms technologies.
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