CONVERTING A 6MM ARC MAGAZINE TO FEED 7.62x39

A previous posting on this site about Ruger’s Ranch rifle chambered for the 7.62x39mm round and a passing mention about converting an AI pattern magazine to work reliably with the little Russian round generated enough interest to be worthy of a follow-up. And so, here’s some more information on converting one of these great magazines to handle a cartridge it was never designed to accommodate.

7.62x39 cartridge. As a result, it’s left to people like myself and others to develop workable conversions of existing magazines to fill the gap. My own requirement for such a conversion stemmed from the desire to put MDT’s TIMBR stock on the previously mentioned Ranch Rifle and to avoid using the factory five-round magazine. It’s not that the factory magazine isn’t reliable, but since it’s the same magazine used in the Mini-30, it has a last-round bolt hold-open feature, which is fine on a semi-auto but totally annoying on a bolt action. So, it had to go.

MDT staff warned me that none of their magazines work reliably with the Russian round, and so I went into this project with eyes wide open. A review of their catalog, which might involve the least work, led me to their 10-round polymer magazine for the 6mm ARC. It’s a round with very similar dimensions, the big difference being the significant body taper in the Russian’s case, which is the bane of reliable feeding. The following images show how the two cartridges stack up and the curved stack that inevitably results from the Russian cartridge. This is why 30-round AK-47 magazines have their distinctive curved shape.

One or two cartridges will feed from the magazine, but load any more than that, and they start to nosedive into the front of the magazine body, tying up the rifle. There’s enough room in the AI magazine to build a filler block with the required curve in it to ensure reliable feeding. Craft a new follower, and it should work fine. And this is what an acquaintance did using a 6 BR magazine shell and spring. The following image shows the basic idea, with the filler block made via 3D printing. He reports that it works just fine in a Savage rifle equipped with an MDT stock and that it takes a full ten rounds.

Lacking a 3D printer, I thought it might be possible to do something simpler, so I added an extra spring to the magazine’s internals. I reasoned that if the rounds were nosing down, applying extra upward force to the front tip of the follower via a coil spring might solve the problem. Fortunately, there’s a gap in front of the follower spring large enough to insert an extra spring of the proper dimensions.

A little digging in a box of miscellaneous springs I keep in my shop turned up a coil spring about 3.75 inches long and with an outside diameter of 0.455 inches. It was a great fit into the previously mentioned gap, and a quick reassembly and test showed I was close to something workable but hadn’t achieved it yet. Turns out the bullet tips were catching on the coil spring, and this interfered with reliability.

The next step was to insert a plug that would act as a guide rod for the coil spring and prevent bullet tips from catching the coils. I made this from a brass rod with an external diameter of .375 inch and a length of 1.63 inches. A taper cut at the upper tip ensures the spring stacks down smoothly when compressed, and a 0.42-inch-diameter rim at the bottom keeps the guide rod in place at the bottom of the coil spring.

Reassembly and further testing showed it all worked surprisingly well. Capacity is limited to six rounds because of the brass guide rod, but that’s a limitation I can live with to use AI magazines and get rid of that annoying last-round bolt hold-open feature. Feed reliability is excellent with the ammo I’m using, and I think it’s a conversion worth trying if you want an AICS magazine to feed 7.62x39. It’s low-cost and doesn’t make any permanent alterations to the 6mm ARC magazine.

Hopefully, the ideas I’ve listed here will be improved upon by other tinkerers or prompt someone to develop a dedicated magazine for the little Russian, something I think is overdue.

ABOUT THE AUTHOR

Al Voth calls himself a "student of the gun." Retired from a 35-year career in law enforcement, including nine years on an Emergency Response Team, he now works as an editor, freelance writer, and photographer, in addition to keeping active as a consultant in the field he most recently left behind—forensic firearm examination. He is a court-qualified expert in that forensic discipline, having worked in that capacity in three countries. These days, when he's not working, you'll likely find him hunting varmints and predators (the 4-legged variety)