Flow-Formed Cobalt Barrels Allow All-Day Machine Gunning

I’m not a metallurgist. Nor do I play one on the Internet. But I know how to cut and paste electronic data. So . . . “If you look at steel in a machine gun environment, it gets very hot at a high rate of fire,” Vinny Leto told army.mil. The Systems Project Engineer at the Armament Research, Development and Engineering Center (Weapons System Technology Directorate) knows the answer to that problem: cobalt. “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.” Unfortunately, “the material, for all of its phenomenal properties, is very difficult to manufacture and machine.” Especially the rifling part of the program. Until now . . .

In flow forming, a cylinder of metal has a hard, preformed mandrel inserted inside it. Then, ultra-powerful rollers squash the cylinder onto the mandrel, so causing the inside to take on the desired shape. The rifling is pressed into the bore, rather than being cut as with a steel barrel.

Leto and his colleagues have apparently made a barrel from 50+ per cent cobalt alloy using flow-forming and test-fired 24,000 rounds through it, causing it to reach temperatures of 1,100 degrees. A steel barrel would have failed under such treatment.

If the manufacturing method proves efficient and cost-effective—a strange concept for the military but there it is–cobalt barrels could eliminate the need to swap out big ass machine gun barrels in combat. A useful time saver I’d say. Just did, in fact. Well, wrote. Soldiers could also shoot their light arms on full auto longer without fear of failure. Although I’m not entirely convinced that that would be such a good thing . . .

comments

  1. avatar TTACer says:

    I wonder how they get the mandrel out.

  2. avatar Evan says:

    Treat it with a release agent (lube) before pressing then twist/pull it out after with heavy machinery?

  3. avatar BLAMMO says:

    I think Ruger hammer-forges their barrels around a grooved mandrel so they don’t have to bore out the blank or rifle it.

  4. avatar GAKoenig says:

    A number of companies hammer forge barrels.

    The process uses a rotary hammer forge; basically a giant machine with a bunch of hammers arranged radially around the center, where the work piece goes. You take a cylinder of metal with a hole in it (roughly the size of the bore) and put it around the mandrel, and the rotary hammers pound on it till it presses close against the mandrel. Said mandrel has all of the rifling features on it (this is how HK and Glock make polygonal rifling).

    The mandrel is removed with a hydraulic ram. During forging, oil is pumped at high pressure between the mandrel and the barrel as it forms. What winds up happening is that hydrostatic pressure actually keeps the barrel from truly contacting the mandrel by a few microns (you can control this by controlling the overall pressure of the oil pump). This also saves on tool wear with the mandrel and insures a high-quality surface on the inside of the barrel. This is also how you can slide the barrel bore blank off of the mandrel without distorting the inside surface.

    Most companies forge relatively long blanks (10″) and cut them a bit larger than the final barrel. This blank barrel is chucked into a couple of lathes so it can be turned to the final profile, attachment fittings machined and the chamber is cut with a high precision reamer at a relatively low speed.

    This is the modern process for barrel making. The old method was a specialized tool called a gun drill and I don’t think anyone makes those anymore. This was a laborious process and the machines required constant tinkering and adjustment. Old school barrel makers are all about the art of using such a tool, but rotary forging is better. The only downside is that the rotary forge is hugely expensive, but can knock out barrels in production VERY quickly.

    1. avatar BLAMMO says:

      Interesting. Thanks for the comprehensive explanation.

    2. avatar phageghost says:

      You still need a gun drill to make the hole, how else are are you going to get the mandrel in there? Hammer forging is a method of adding the rifling, the main alternatives (still quite common) are cut rifling and button rifling.

  5. avatar Joseph Bagdal says:

    Oil under pressure is, “hydraulic”, not, “hydrostatic”! A standing tank of liquid has hydrostatic pressure on the inside of the vessel. A closed tank with a pump attempting to force a liquid into the tank has hydraulic pressure on the inside of the vessel.

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