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The Semi Auto MK 760

By Brian Zuzelo
Photos By Christine Hill

The MK Arms Model 760 SMG is known throughout the Class III community as an affordable and transferable clone of the Smith and Wesson M-76. The MK-760 SMG has received mixed reviews from many Class III enthusiasts. Some claim that weapon needs several modifications to critical parts to be considered reliable, while others have said their MK-760 ran perfectly out of the box. One difference between the MK-760 and S&W M-76 is that the MK-760 has a series of semiautomatic-only versions. Michael Rupplinger, founder and owner of MK Arms, created a semiautomatic carbine and pistol version of his MK-760, so those unable to own the SMG could enjoy the next best thing. The pistol and carbine versions were held to the same standards of quality as its full-auto variant. However, due to legal issues, as well as a number of setbacks for the company, these semiautomatic-only versions of the MK-760 never enjoyed much commercial success. The closed-bolt configurations of this weapon, however, have enjoyed a relatively high collector’s status and are fun to shoot.

During the Viet Nam war, the Carl Gustof Model 1945, or “Swedish K,” was an exceptionally popular submachine gun. It was praised for it’s reliability and it’s optimal cyclic rate of 600 rpm. The weapon could be found in the hands of Special Forces units and Navy Seals alike. This high quality post-war design could be had at surplus prices and were purchased to arm ARVAN forces in South Vietnam. The US Navy expressed interest in procuring a number of Model 1945s from the Swedish government, but were denied because of Sweden’s declared neutrality*. Smith & Wesson was then approached to create a weapon of similar quality are reliability. After a year and a half of design, S&W introduced the Model 76. The Model 76 incorporated most of the positive attributes of the Swedish K, such as compactness of the folding stock as well as the overall simplicity of the weapon. Close to 6,000 Model 76s were produced between 1967 and 1974*. The US Navy was then no longer interested in keeping the weapon as a part of its arsenal, and discontinued orders for the weapon after the Vietnam War. The Navy’s SEAL units were the only US military force to continue using the M76 after that date. Subsequently, a large number of M-76’s found there way into Police Department arsenals during the late 1970’s.

Because S&W discontinued the weapon and was no longer making parts, SEAL units and police departments were faced with the problem of repairing broken and worn parts.

In 1980, Mike Ruplinger and Kenneth Domenick of MK Arms began production of replacement parts for the S&W M-76. MK Arms contracted with Seal Team One, based in Coronado, California (the Naval Amphibious Base), to make replacement parts for the S&W M76’s used in training. The company supplied spare parts and magazines for SEAL Team One until the H&K MP5 became the unit’s submachine gun of choice in the early 1980’s. After the need for spare parts by the US Navy became non-existent, Ruplinger and a new partner, Duane Carlson, began to invest all of their energy into producing their own M-76 clone for the growing Class III market.

MK Arms began production of the MK-760 SMG in full force before the enactment of the Gun Owner’s Protection Act’s (May 19, 1986) and the company was then no longer be allowed to manufacture fully automatic firearms for civilian use. MK Arms produced approximately 1,500 select fire MK-760s in the final weeks before the machine gun ban. The round-the-clock operations helped produce some of the last transferable machine guns allowed on the civilian market. The MK-760 SMG was offered for the suggested retail price of $795, and came in either a gray parkerized or black crinkle epoxy finish. The semiautomatic-only carbine and pistol was offered with similar options and were available from the company for $495.

The semiautomatic-only MK-760 carbine utilized most of parts from the SMG, with the exception of the bolt, lower receiver, and 16” barrel. The MK-760 pistol was simply the same design as the carbine sans the gun’s folding stock and utilized the SMG’s 8-inch barrel. The semiautomatic-only weapons accepted the MK-760 and S&W M-76 magazines without alteration. At close to 7.5 pounds unloaded, the MK-760 pistol is a true heavy weight. The MK-760 out weighed all other “assault pistols” in its class, such as Intratec and Cobray pistols. The semiautomatic-only series of weapons were offered with a 14-round magazine with the option of purchasing a 24- or 36-round magazine. Carrying cases and magazine pouches with the MKA logo were also optional. The original design of the semiautomatic-only series fired via the open-bolt principle and the first commercially produced weapons were in fact open-bolt guns. MK Arms claimed that they had received permission by the BATF to produce the semiautomatic-only open-bolt guns after submitting a sample weapon to the Technical Branch of the BATF. However, the BATF deemed the early production MK-760 semi-auto series illegal because of the open-bolt deign and that the weapons violated the 1982 BATF ruling on open bolt semi-autos. The remaining inventory of open-bolt semiautomatic-only weapons MK Arms had in storage were either converted for sale as a SMG before 1986 or kept for parts for their new semiautomatic-only design.

Mike Ruplinger decided to enlist the help of Tim LaFrance of LaFrance Specialties to redesign critical parts for the semi-auto MK-760 carbines. LaFrance assisted in altering the design of the semiautomatic-only bolt and lower receiver. MK Arms produced the closed-bolt semiautomatic-only carbines with all modifications needed to keep the weapon in compliance with BATF standards. The guns came with a carrying case and a small bag of spare parts, which included a firing pin, extractor, and firing pin spring. The newly designed carbines did not meet with great commercial success. The carbines were produced in low numbers, (less than 750 carbines and pistols total) due to the financial and legal woes of MK Arms. MK Arms hoped that the sales of its semiautomatic-only weapons would help the financially ailing company. Unfortunately, this was not the case for MK Arms, and the company closed its doors in 1989 after the death of partner Duane Carlson. Tim LaFrance acquired the remaining inventory of MK Arms, which included the parts for the MK-760 SMG, but did not include the semiautomatic-only parts for the closed-bolt carbine. LaFrance continues to offer gunsmith services for the select fire MK-760 SMG and offers a one-year warrantee on all of his work.

The MK-760 semiautomatic-only carbine embodies most of the positive traits the S&W M76 has, which are overall simplicity of manufacture, ergonomics and ease of assembly and disassembly. The weapon enjoys a rugged construction and it’s folding stock locks up in a solid manner with very little wobble at all during firing. Barrel removal and installation can be done easily by hand by removing the slotted barrel shroud, which firmly locks onto the receiver of the weapon. A standard 8-inch SMG barrel shroud was issued with the semi-auto carbine, but a 16-inch barrel shroud was available on a request-only basis from MK arms.

The sights on the weapon are very basic, a guarded rear peep sight with a guarded front post sight. The sights would be considered unacceptable by today’s tactical standards, as they do not allow for much adjustment. The carbine can shoot between 3-5 inch groups at 50 yards with iron sights. I have found that Winchester white box and PMC brand, standard 115-grain 9mm ball ammo worked very well in the carbine. The weapon’s main shortcoming is the trigger pull. The trigger pull on my carbine is close to 13 pounds. This weight makes quick and accurate follow up shots very difficult. Due to the strength of the recoil springs in the semi-auto design, the weapon is also very difficult to cock. This proves to be especially difficult when trying to safely clear a jammed round from the weapon. The magazine lock-up is fairly positive and the weapon’s safety is reliable.

If you purchased a MK-760 carbine or pistol brand new in 1986, a small bag with spare parts (a firing pin and spring, and an extractor) was packaged in the factory box. Those buying them on the second hand market will have a difficult time finding spare parts. However, the extractor from the full-auto will work in the semiautomatic-only model. However, most parts in the bolt assembly and lower receiver are different than the full-auto version of the gun. Scott Andrey of Scott Andrey Machine manufactures a number of parts for the full auto MK-760 and does custom work on request. He created a semiautomatic-only firing pin for my MK-760 carbine using the original as a template. Scott has a number of custom-made parts and accessories for the MK-760, which includes 16-inch carbine barrels and 16-inch shrouds.

The semiautomatic-only MK-760 carbine and pistol are unique weapons because they are the only weapons in semiautomatic-only of their type. They are the only semiautomatic-only weapons produced in moderate numbers that resemble the Swedish K and S&W M76. In the early 70’s, the MAC Corporation did produce an open bolt semiautomatic-only Swedish ‘K’ that was made in extremely limited numbers, and these weapons have faded into obscurity. The semiautomatic-only MK-760 is a true gem for collectors because of their limited production numbers. They usually command a $800-$1,200 price tag, depending upon the available accessories and condition of the weapon. Magazines for this weapon usually run between $90- $125. The price and availability of parts for the semiautomatic-only MK-760 have put the weapon in the class of a collectable rather than a shooter. The weapon’s design problems and series of unfortunate circumstances at MK Arms hindered the sale of the semiautomatic-only MK-760 series. However, MK Arms was able to fill the void in the subgun clone market with these interesting and collectable weapons.

Update: At the time of the writing of this article Omega Arms has released their post-ban semiautomatic-only clone of the S&W M76 called the Omega 76. Special Weapons LLC has contracted to make the first 150-250 guns and then Omega Arms will assume production. All inquires may be directed to Tach Weapons Training at 480-221-1525 or Omegaarms@aol.com.

*Information taken from “The Wold’s Machine Pistols and Submachine Guns Vol. IIa” by Thomas B. Nelson and Daniel D. Musgrave. Available from Ironside International Publishers, Inc.

Scott Andrey Machine
108 Beaufort Road
Dept. SAR
Fremont, NC 27830
(919) 242- 6334 Evenings, EST

LaFrance Specialties
Box 87933
Dept. SAR
San Diego, CA 92138
(619) 293-3373.


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