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History and Function of Counter-Balanced Assault Rifles


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At the end of January, 2018 and after many false starts, the Russian military formally announced the limited adoption of the AEK-971 and AEK-973 rifles.  These rifles feature an unusual counterbalanced breech mechanism which is intended to improve handling, especially during full auto fire.  While exotic outside of Russia, these counter-balanced rifles are not at all new.  In fact, the 2018 adoption of the AEK-971 represents the first success of a rifle concept that has been around for a some time.

Earliest Origins

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Animated diagram of the AK-107/108

 

Balanced action recoil systems (BARS) work by accelerating a mass in the opposite direction of the bolt carrier.  The countermass is of similar mass to the bolt carrier and synchronized to move in the opposite direction by a rack and pinion.  This cancels out some, but not all of the impulses associated with self-loading actions.  But more on that later.

Long before Soviet small arms engineers began experimenting with BARS, a number of production weapons featured synchronized masses moving in opposite directions.  Generally speaking, any stabilization that these actions provided was an incidental benefit.  Rather, these designs were either attempts to get around patents, or very early developments in the history of autoloading weapons when the design best practices had not been standardized yet.  These designs featured a forward-moving gas trap that, of necessity, needed its motion converted into rearward motion by either a lever or rack and pinion.

 

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The French St. Etienne Machine Gun

 

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The Danish Bang rifle

 

At around the same time, inventors started toying with the idea of using synchronized counter-masses deliberately to cancel out recoil impulses.  The earliest patent for such a design comes from 1908 from obscure firearms designer Ludwig Mertens:

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More information on these early developments is in this article on the matter by Max Popenker.

 

Soviet designers began investigating the BARS concept in earnest in the early 1970s.  This is worth noting; these early BARS rifles were actually trialed against the AK-74.

 

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The AL-7 rifle, a BARS rifle from the early 1970s

 

The Soviet military chose the more mechanically orthodox AK-74 as a stopgap measure in order to get a small-caliber, high-velocity rifle to the front lines as quickly as possible.  Of course, the thing about stopgap weapons is that they always end up hanging around longer than intended, and forty four years later Russian troops are still equipped with the AK-74.

A small number of submachine gun prototypes with a BARS-like system were trialed, but not mass-produced.  The gas operated action of a rifle can be balanced with a fairly small synchronizer rack and pinion, but the blowback action of a submachine gun requires a fairly large and massive synchronizer gear or lever.  This is because in a gas operated rifle a second gas piston can be attached to the countermass, thereby unloading the synchronizer gear.

There are three BARS designs of note from Russia:

AK-107/AK-108

 

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The AK-107 and AK-108 are BARS rifles in 5.45x39mm and 5.56x45mm respectively.  These rifles are products of the Kalashnikov design bureau and Izmash factory, now Kalashnikov Concern.  Internally they are very similar to an AK, only with the countermass and synchronizer unit situated above the bolt carrier group.

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Close up of synchronizer and dual return spring assemblies

This is configuration is almost identical to the AL-7 design of the early 1970s.  Like the more conventional AK-100 series, the AK-107/AK-108 were offered for export during the late 1990s and early 2000s, but they failed to attract any customers.  The furniture is very similar to the AK-100 series, and indeed the only obvious external difference is the long tube protruding from the gas block and bridging the gap to the front sight.

 

The AK-107 has re-emerged recently as the Saiga 107, a rifle clearly intended for competitive shooting events like 3-gun.

 

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AEK-971

The rival Kovrov design bureau was only slightly behind the Kalashnikov design bureau in exploring the BARS concept.  Their earliest prototype featuring the system, the SA-006 (also transliterated as CA-006) also dates from the early 1970s.

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Chief designer Sergey Koksharov refined this design into the AEK-971.  The chief refinement of his design over the first-generation balanced action prototypes from the early 1970s is that the countermass sits inside the bolt carrier, rather than being stacked on top of it.  This is a more compact installation of the mechanism, but otherwise accomplishes the same thing.

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Moving parts group of the AEK-971

The early AEK-971 had a triangular metal buttstock and a Kalashnikov-style safety lever on the right side of the rifle.

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In this guise the rifle competed unsuccessfully with Nikonov's AN-94 design in the Abakan competition.  Considering that a relative handful of AN-94s were ever produced, this was perhaps not a terrible loss for the Kovrov design bureau.

After the end of the Soviet Union, the AEK-971 design was picked up by the Degtyarev factory, itself a division of the state-owned Rostec.

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The Degtyarev factory would unsuccessfully try to make sales of the weapon for the next twenty four years.  In the meantime, they made some small refinements to the rifle.  The Kalashnikov-style safety lever was deleted and replaced with a thumb safety on the left side of the receiver.

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Later on the Degtyarev factory caught HK fever, and a very HK-esque sliding metal stock was added in addition to a very HK-esque rear sight.  The thumb safety lever was also made ambidextrous.  The handguard was changed a few times.

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Still, reception to the rifle was lukewarm.  The 2018 announcement that the rifle would be procured in limited numbers alongside more conventional AK rifles is not exactly a coup.  The numbers bought are likely to be very low.  A 5.56mm AEK-972 and 7.62x39mm AEK-973 also exist.  The newest version of the rifle has been referred to as A-545.

AKB and AKB-1

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AKB-1

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AKB

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AKB, closeup of the receiver

The AKB and AKB-1 are a pair of painfully obscure designs designed by Viktor Kalashnikov, Mikhail Kalashnikov's son.  The later AKB-1 is the more conservative of the two, while the AKB is quite wild.

Both rifles use a more or less conventional AK type bolt carrier, but the AKB uses the barrel as the countermass.  That's right; the entire barrel shoots forward while the bolt carrier moves back!  This unusual arrangement also allowed for an extremely high cyclic rate of fire; 2000RPM.  Later on a burst limiter and rate of fire limiter were added.  The rifle would fire at the full 2000 RPM for two round bursts, but a mere 1000 RPM for full auto.

The AKB-1 was a far more conventional design, but it still had a BARS.  In this design the countermass was nested inside the main bolt carrier, similar to the AEK-971.

Not a great deal of information is available about these rifles, but @Hrachya H wrote an article on them which can be read here.

 

 

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  • 2 months later...

Good overview, nice to see people actually doing their research. Balanced recoil system is a simple, yet amazing concept, and recently I tried to document the history of civilian Saiga 107 - mostly what I saw myself in the last few years: https://www.thefirearmblog.com/blog/2018/06/11/balanced-recoil-sporting-rifles-a-brief-history-sr-1-saiga-107-ak15/

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  • 2 weeks later...
On 4/27/2018 at 6:28 AM, Akula_941 said:

any infor for AO-38M and AG-021?

 

 

Sadly, I don't have good sources on the more obscure Soviet rifle prototypes.

 

I'm very curious if they made any counterbalanced designs that were something other than AK guts with a counterbalance mechanism stapled to it.

This pistol design is essentially a counterbalanced blowback mechanism.

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