What are the most widely distributed, automatic, small arms operating systems in use today? By the sheer number of arms produced and fielded, the winner would have to be the gas driven piston-bolt carrier- rotating bolt system seen most commonly in the AK-47 and its derivatives and in the M16/AR-15 family. Coming in a strong second would be the retarded, blowback, roller-locked system, refined by engineers working at Mauser during WWII, and incorporated in such well known designs as the CETME, G3, MP5, HK91, HK93 and others.
Century International Arms originally brought us a semi-automatic CETME in 7.62 NATO. CIA has now downsized the design in the more popular 5.56 NATO caliber and designated it the Model, C93. Heckler and Koch did something similar when they downsized the G3 to 5.56mm caliber dimensions and imported it into the United States as the semi-automatic Model HK93.
Between 1974 and 1989, approximately 18,000 HK93s were imported into the US. The retail price of an HK93A2 (fixed stock) in 1985 was $599. If you can find one today, expect to pay $2,000 to 3,000 for the privilege of ownership. A matching bayonet will fetch up to $150. Or you can buy a Century International Arms C93 with an original G3/HK91 bayonet for approximately $550 at your dealer or on Internet auction sites like Gun Broker. The C93 sports a new receiver and barrel, but most of the other parts are derived from original HK33 parts kits. The C93 is simply a terrific bargain as well as a neat handling and accurate milsurp era 5.56mm firearm.
The history of the roller-lock, retarded, blowback operating system is fascinating. The system design was perfected by Mauser engineers and incorporated in part as the locking system for the German MG42 machine gun and a prototype assault rifle, the StG-45. Being a recoil operated system, rather than gas operated, the system is simplicity itself and reliable. Yes, it’s simple but deceptively complex from an engineering perspective.
The roller-locking bolt of the C93 is composed of two interlocking assemblies—a hollow front unit that incorporates the bolt face, extractor and two rollers—and a heavier rear unit that holds a spring loaded firing pin retained by a rectangular piece that carries two sloping cams. The rear assembly slips into the hollow housing of the front bolt head, and the bolt head is rotated to lock both assemblies together.
As the front section of the bolt picks up a cartridge and chambers it, the heavier rear assembly is slammed into battery by the mainspring. The tapered cams on the firing pin retainer engage the rollers, forcing them into their respective locking recesses in the walls of the receiver trunnion.
At the instant of firing, the rollers are firmly locked into battery. At a millisecond point in the pressure time curve following ignition, the pressure has dropped and the case, floating on a film of gas in the fluted chamber, pushes sufficiently back against the head of the bolt to force the front bolt head assembly backward. This moves the rear section of the bolt, held in place only by the pressure of the mainspring, rearward, thereby camming the rollers out of their respective locking recesses.
The extraction cycle is fast, abrupt and since the fired case is not rotated or eased back slowly during the initial extraction phase, the engineers had to come up with a solution so that case heads were not ripped off. The solution was to flute the chamber so that the case was loosened from the walls of the chamber by a film of gas. The system works, although the cases come out striped with carbon deposits. C93 fired cases can be full length resized and reloaded, but only after carefully inspecting the area of the case head and web to insure there are no signs of an incipient head separation.
The keys to maintaining the reliability of a roller-lock system are to keep that fluted chamber clean and to keep the bolt assemblies well lubricated. Another consideration is that the C93 doesn’t have a gas regulator so some cartridge brands, bullet weights and powders will do better than others in terms of cycling the system and delivering superior accuracy. In that regard, I consider the design a bit more finicky about ammunition than the average gas-driven system. You just have to experiment. Finally, when you pull that operating handle back and compress the mainspring, let the handle fly forward to charge the rifle. If you ride it down, the roller-locks will not seat in their recesses and all you’ll hear when you squeeze the trigger is a dreadful “click.”
The C93 has a 1:9″ twist barrel. I thought loads in the 52- to 55-grain range would be ideal; however, the sweet spot for the C93 I tested was the 69-grain match bullet, specifically DoubleTap’s 69-grain HP Boat tail Match load that is rated at 3,015 fps from a 22″ barrel. Using the diopter sight of the C93 at 50 yards, my 5-shot groups averaged 1-1/2″ with DoubleTap’s 69-grain match load, and the rifle cycled perfectly.
The sights of the C93 consist of a front, fixed, hooded post and a HK-type rotating diopter rear sight. The diopter sight is adjustable for windage and elevation. Check eBay for an “HK drum sight adjustment tool” to set the elevation. Rotated, the diopter drum offers four sight options—an open “V” for very close engagements and three different sized apertures. It’s a functional sight system, and those apertures are a blessing given the short 16-1/4″ barrel and the 19″ sight radius of the C93.
The receiver will accept an HK-type clamp on scope mount that you can find on the Internet, but scoping this handy, little rifle that already weighs 8.2 pounds unloaded is questionable at best.
The integral carrying handle of the C93 is a neat and useful part of the design as is the one pin takedown of the C93. Push out that pin located at the juncture of the butt and the receiver, and the C93 just falls apart in your hands
The C93 comes with two 40-round alloy magazines. If you need more, Century International Arms has an armful of original HKs at $19.87 each. They’re a snug fit in the receiver well and need to be rocked into place.
The fire control system consists of a polymer shell with metal parts inside. The trigger pull on my test C93 averaged 9 pounds, 5 ounces on a Lyman electronic scale. It’s a bit creepy, but fully manageable.
I like the CETMEs and the HK variants. They are tough, robust battle rifles that can be disassembled in seconds to keep them clean and operating. Century International Arms C93 upholds that tradition, and it’s as close as most of us will ever come to owning an HK93.
By Holt Bodinson
Century International Arms Model C93
MAKER: Century International Arms
430 S. Congress Ave., Ste. 1
Delray Beach, FL 33445
ACTION TYPE: Roller-lock, retarded, blowback, semi-automatic,
CALIBER: 5.56 NATO
BARREL LENGTH: 16-1/4″
OVERALL LENGTH: 36-1/2″
WEIGHT: 8.2 pounds
SIGHTS: Rotary diopter rear; fixed front post
646 S. Main St., #333
Cedar City, UT 84720
“The World’s Assault Rifles” by Gary Paul Johnston and Thomas B. Nelson. Hardcover, 1216 pages @2010, $74.95 From: A&J Arms Book Sellers, 2449 N. Orchard Ave., Tucson, AZ 85712. (520) 512-1065
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