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The author bought a Mini-14 soon after its introduction and immediately installed a variable 3x-to-9x optical sight. He still owns it and it has served him well. Its five shot group accuracy, with military ball ammunition, is on the order of 1.5 inches at one hundred yards. Serious riflemen sneer at this degree of accuracy of course. Remember though, this is an outof-the-box semiautomatic rifle, using lessthan-the-best ammunition and it has met the author’s needs for thirty-plus years. Reliability-wise, nothing could have been better than his Mini-14. When using a genuine Ruger manufactured magazine, the author has never experienced a failure with it. A fully automatic version of the Ruger Mini-14 was also introduced. The basic blue-steel model was called the AC-556. Another model was available that accepted a standard M7 bayonet and was designated AC-556GB (“GB” for government bayonet). A very compact version of the AC-556 was soon added to the Ruger product line.

It has been over thirty years since Sturm, Ruger, & Company introduced a semiautomatic 5.56x45mm (5.56 NATO) carbine. It looked like a small version of a US Army M14 and it was, in fact, called a “Mini-14.” The Ruger carbine was an immediate sales success and it has been in continuous production since its introduction. It had a thirteen inch barrel and a side-folding stock. This model was called the AC556K.” It is assumed that the “K” in the compact version’s designation stands for the German word “Kurtz,” meaning “short.” If a 13-inch barrel AC-556K is placed into a standard AC-556 stock, the result is a very short select-fire carbine that points very naturally. Before long, AC-556s became available in stainless steel versions. The prefix “K” was added to the designation of those that were made of stainless steel and thus became the KAC-556 and KAC-556K if it was the short barreled version with sidefolding stock.

In addition to their fire control selectors, full-auto Ruger carbines had flash hiders that served a dual purpose. Besides the obvious function of shielding muzzle flash, it also served as a rifle grenade launching fixture. When launching a rifle grenade, a special type of blank cartridge is used to propel the grenade. The safety on the full-auto AC-556 Ruger carbine is ergonomically located within the trigger guard. This is the same location as found on the M1 Garand and the M14. The fire control selector on the AC556, like the M14’s, is located above the trigger on the right rear side of the receiver.

Top, the author’s thirty-year-old Ruger Mini14. It has not malfunctioned in thirty-plus years. Bottom, a Ruger KAC-556GB.

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Right: Three Ruger AC-556 fire control selectors. The top one is set to semiauto. The middle one is set to three-round-burst. The bottom one is set to full-auto. The selector has a locking button on top that assures that the AC-556 remains in the user-selected mode of fire. The button must be pressed downward in order to reposition the selector. Unlike an M14, an AC-556 fire control selector has three firing modes: semiauto (straight up), three-round-burst (midposition) and full-auto (horizontal). The semi-auto and full-auto selector positions are self explanatory. The three-round-burst position needs some further discussion though. Due to the way in which it functions, when the burst is first selected, it does not always produce a three-round burst. Depending on the circumstances, the selector can produce bursts of one, two or three rounds on the first pull of the trigger. This is not generally a problem but an explanation is in order. When an AC-556 is fired in either semi, burst or full-auto, a pawl engages and advances a ratcheting round-counter. When burst is selected and the roundcounter reaches its third step, the AC-556 disconnector is engaged to prevent another shot. The explanation for the uncertain burst becomes clear upon reflection. Though the round-counter is disengaged from the disconnector when either semiauto or full-auto is selected, the roundcounting pawl is never disengaged from the trigger. It counts the fired rounds in the semi-auto and the full-auto modes as well. As a result, when burst is engaged, the round-counter could be resting on either its first, second or third step. The first pull of the trigger after burst is selected could

produce a burst of one, two or three rounds. After firing the first burst in the burst mode, the round-counter will become properly synchronized. All subsequent bursts will then be of three rounds unless the trigger is released before the disconnector ends the burst. At the AC-556’s relatively slow cyclic rate of 750 rounds per minute (rpm), with just a little practice a shooter can set the selector to full-auto and fire two, three or four founds at will. Few experienced AC-556 shooters use the burst position of the selector. Magazines Genuine Ruger AC-556 magazines are produced in capacities of five, twenty and thirty rounds. Like the detachable box magazines of most modern rifles, AC-556 magazines are of the staggered column, left/right feeding design. They are very reliable and easy to load. Other manufacturers have produced magazines for the AC-556. Some of these have proven to be just as reliable as genuine Ruger magazines. Others have been less reliable. In the author’s experience, magazines that were made for the AC-556 by Ramline and Thermold have proven themselves to be nearly equal to genuine Ruger magazines. Two 90-round magazines have been made for the AC-556. The one made by M.W.G. is nothing more than a very long staggered column magazine that has been twisted into a left-offset circle. Loading it

begins easily but it becomes difficult after inserting approximately fifty rounds. The M.W.G. 90-round magazine seems to have more internal friction than other staggered column, left/right feeding magazines. This is evidenced by the AC-556 operating springs’ lack of sufficient force to reliably strip the first ten rounds from a fully loaded M.G.W. magazine. For the first ten rounds, the AC-556 bolt stops with a round only

Below: From left to right are: An M.W.G. 90-round drum magazine; an AK47 90-round drum that was converted prior to the HICAP ban for use in an AC-556; a Thermold 30/40-round AC-556 magazine; A Thermold 30-round AC-556 magazine; A clear plastic Ramline AC-556 magazine; Ruger 30, 20 and 5-round AC-556 magazines.

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Above: Two 90-round magazines and 90-rounds of loose ammo. The AK47/AC-556 magazine is on the right and the M.W.G. magazine is on the left. partially pushed into its chamber. To continue firing, it is necessary to manually push the bolt closed. During the next ten rounds, occasional failures of this type continue to occur. No failures of the M.W.G. magazine were experienced if only seventy rounds were loaded into it. Considering the difficulty of loading the last twenty rounds, even if the M.G.W. magazine fed rounds 71-90 reliably, most shooters would probably elect to load only seventy. More evidence of the M.W.G. 90round magazine’s high internal friction is the slower AC-556 cyclic rate while using it. When using a Ruger 20-round magazine, the AC-556 cycles at 750 rounds per minute (rpm). When the M.W.G. magazine is loaded with seventy rounds, the initial cyclic rate is only 500 rpm. The cyclic rate increases to 700 rpm as it fires the last thirty rounds in the M.W.G. 90-round magazine. The M.W.G. magazine is asymmetri-

cal. This causes a little unbalance but it is not a problem for a right-handed shooter. The left-side offset magazine is cradled and supported in the shooter’s left arm when firing in the standing-position. Another manufacturer made a 90round magazine for the AC-556 by grafting the upper portion of a Ruger magazine to an AK47-type drum magazine. The staff portion of this magazine is centrally located causing the AC-556 to balance well. Like the drum magazines of Suomis, Thompsons and PPSh41s, the ammunition in the AK47/AC-556 drum is stacked in a long, circular, single column. All other AC556 magazines are of the two column type. An AK47/AC-556 drum loads and functions like a Thompson drum magazine. Whereas a Suomi or a PPSh41 drum is wound before it is loaded, an AK47/AC556 and a Thompson drum magazine is wound after it is loaded. In theory, this is an advantage as a drum magazine of this type may be stored loaded but unwound

An assembled (left) and disassembled (right) gas block.

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for long periods without stressing the magazine spring. Like the M.W.G. 90-round magazine, the AK47/AC-556 drum magazine has more internal friction than a genuine Ruger 20-round magazine. When using the AK47/AC-556 90-round drum magazine, the AC-556 cyclic rate is slowed to 650 rpm but, unlike the M.G.W. 90-round magazine, the cyclic rate is nearly constant. The author was unable to wind his AK47/AC-556 drum magazine’s operating spring sufficiently to permit it to fire all 90 rounds. After firing about 50 rounds, the AC-556 would stop with its bolt closed on an empty chamber. This condition indicates that the drum magazine’s operating spring is unable to elevate a fresh round before the fast-cycling bolt closes. When this occurs, firing can be resumed by rewinding the magazine spring and recycling the bolt. 7.62x39mm Conversion The semi-automatic Ruger Mini-14 is also offered for sale in the Soviet AK47 caliber of 7.62x39mm. Supplies of this ammunition have been plentiful and cheap. The full automatic AC-556 is not manufactured in this caliber though. Can one be converted to 7.62x39mm caliber? Yes, it is possible but there are considerations that make this conversion impractical. Ruger will sell neither a 7.62x39mm barrel nor a bolt unless they also install it in the firearm themselves. More importantly, Ruger will not make this caliber conversion for an AC-556 owner. For those who are determined to have an AC-556 in 7.62x39mm, the most practical way is to

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buy a Mini-14 in this caliber in order to acquire the needed parts. The skills of a competent gunsmith would be required to install the barrel. There is also a very practical reason for not converting an AC-556 to 5.56x39mm. To avoid the complications that were caused by the onerous provisions of the Magnuson-Moss Act (Public Law 93-967), Ruger sells its firearms without a written warranty. Ruger has a reputation though for repairing all unmodified Ruger firearms without charge. Ruger would not repair a caliber-converted AC-556 either gratis or for pay. Of course, the BATF would have to be notified as well of any changes in barrel length or caliber since this is not a “drop-in” and easily removed alteration. An AC-556 owner should give all this careful consideration before making a conversion to this caliber. .22 Rimfire AC-556 Conversion Due to the 5.56mm NATO round’s long range and deep penetration, extra care must be taken when selecting a place to shoot. It must have a very good backstop and a large unoccupied safety area located behind it as well. Additionally, when compared to a pistol caliber, the 5.56mm NATO round is very loud. For these reasons, a backyard shooting range is generally unsuitable for the AC-556. A simple solution is available though. Jonathon Arthur Ceiner manufactures and sells a .22LR conversion kit for the Ruger AC-556. With certain brands of high velocity .22LR ammunition, it functions well in all three modes of fire. Moreover, the .22LR caliber conversion kit uses the

Cleaning the orifices in the AC-556 gas piston with a 1/16 and 1/8 inch drill bits. The small gas port bushing (upper right) is cleaned with a 1/16 inch drill bit.

standard AC-556 barrel. If it is ever necessary to return the AC-556 to Ruger for repair, the Ceiner .22LR conversion kit can be removed quickly and the original 5.56 NATO parts reinstalled. The .22LR kit is packed in a sturdy plastic storage case. It installs in the AC556 using only a 5/32 Allen wrench and the wrench is supplied with the kit. Ceiner’s installation instructions are complete and relatively simple though first time installation is a learning experience requiring about twenty minutes. Subsequent installations take less than ten. Ceiner’s AC-556 .22LR conversion kit is priced reasonably at $129. Unfortunately, unless the buyer is a law enforcement officer, only 10 round magazines are available for it at this time due to the

HICAP magazine ban. If the HICAP ban is allowed to sunset, the 30-round magazine will once again be available. Fortunately, the author bought his .22LR conversion kit and five extra 30-round magazines long before the HICAP ban was enacted. The AC-556 cyclic rate with .22 CCI Mini-Mag ammunition was 1,340 rpm. At this fast rate of fire, the three-round burst feature proved to be very useful. When firing at 25 yards (23 meters) with threeround bursts, the .22LR AC-556 was very controllable. Most of the hits were contained within a 3.5 inch (89 mm) circle. Initially, the Ceiner .22LR conversion kit functioned very well. After about 2,000 rounds though, stoppages began occurring. In nearly every stoppage, the round struck the face of the barrel slightly above the chamber. These failures occurred with all five 30-round magazines. A thorough cleaning was no help. As good fortune would have it, the author had one Left: When reassembling an AC-556, make certain the “link positioner assembly” (the part with the Ushaped notch at arrows) is in its most vertical position. The assembly on the right is correct.

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A disassembled KAC-556GB

remaining 30-round .22LR magazine that had never been used. It was the one that was originally supplied with the Ceiner .22LR kit and it had never been removed from the storage case. With this magazine, the .22LR AC-556 functioned again with near perfection. A dial caliper was used to compare the one functioning magazine with the five now unreliable ones. The only major difference between them was the gap between the new and well-used magazines’ feeding lips. The functioning magazine’s feeding lip gap measured 0.17 inch (4.32 mm). The same measurements on the non-functioning magazines were all greater than 0.21 inch (5.33 mm). The magazine follower was removed before adjusting the feeding lip gap. A vice was then used to carefully close the feeding lip gaps of the unreliable magazines. It was found that the well-used magazines would function again when their lip gaps were set in the range of 0.16 inch (4.1 mm) and 0.20 inch (5.1 mm). To achieve proper functioning, it is

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necessary for the feed lips to be parallel with a constant gap width. For this reason, avoid using pliers or a hammer to close the gap. Further testing revealed that the .22LR magazine lip gap problem can be avoided entirely if the 30-round magazine is only loaded with 25 rounds. Loading the last five rounds into the magazine requires considerably more effort than loading the previous twenty-five. The extra tension, caused by the last five rounds, seems to be the culprit in spreading the magazine lips. Bolt Bounce All .22LR semi-autos fire from an unlocked breech. The mass of the bolt and the resistance of the operating spring keep the bolt closed during the high-pressure portion of the firing cycle. After the bullet exits the barrel, the residual gas pressure pushes the bolt rearward and compresses the operating spring. The compressed operating spring then pushes the bolt forward, stripping a fresh round from the magazine

and driving it into the chamber. When the rapidly moving bolt strikes the face of the breech, it bounces back a short distance. The pressure of the compressed operating spring restrains the bolt and quickly pushes it back into battery. Bolt bounce occurs in all semi-auto .22LR firearms. While it is not a problem in semiautomatic fire, it is a problem in full automatic fire. In a semi-auto, the bolt bounces out of battery and is then pushed back into battery before the semi-auto shooter can release the trigger and pull it again. On a full-auto .22LR firearm though, the sear releases the hammer as the bolt reaches battery. If nothing prevents the bolt from bouncing back, the hammer will strike the bolt as it bounces out of battery. A misfire often occurs because much of the falling bolt’s energy is absorbed when it strikes the out-of-battery bolt. All reliable closed-bolt .22LR machine guns, except the Ceiner .22LR/AC556, have a moving anti-bounce weight located on the bolt. A microsecond after the bolt strikes the breech; the moving weight strikes the bolt and absorbs the rebounding bolt’s energy, thus preventing the bounce. There is no obvious explanation as to why the Ceiner AC-556 .22LR conversion kit works so well without an anti-bounce weight. The answer may be the AC-556’s massive coil hammer spring. It is much stronger than the hammer spring of an M16. The AC-556 hammer spring seems to overcome bolt-bounce with brute force. It appears to push the bouncing bolt back into battery while retaining sufficient energy to crush the priming compound in the cartridge rim.

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A New Problem is Discovered After shooting .22LR cartridges in an AC-556, thoroughly clean the chamber before firing any 5.56mm NATO rounds. The chamber may have accumulated debris that could prevent the bolt from closing properly. Firing a high-pressure 5.56mm NATO round out of battery is dangerous. Cleaning the AC-556 chamber is not difficult and an M16 chamber cleaning brush or a .357 pistol brush work well. If the AC-556 .22LR kit is shot a lot, the gas port will become blocked with vaporized lead and unburned powder. This blockage does not affect the .22LR kit’s functioning as the kit does not use the AC556 gas system. It is self contained and operates on the “blow back” principle. After the author removed his .22LR kit and reinstalled the 5.56mm NATO parts, the AC-556 would not function unless he cycled the bolt like a straight-pull bolt action rifle. Before it would function again in semi or full-auto, it was necessary to disassemble the AC-556 gas system and clean it. Begin by following the AC-556 owner manual’s disassembly steps. Some Ruger AC-556 owners may not have an owner’s manual. Most of the AC-556s that are in private hands came from police departments when they traded them in for newer guns. Only rarely were the owners’ manuals passed along with the firearms in trade. This is not a problem as the Ruger Corporation wants every one to know how to use their guns safely. AC-556 owners who lack a manual for their AC-556 can get one free. Write Ruger and politely ask for one and enclose a copy of your Form 4. When beginning AC-556 disassembly, do not overlook one very important step. Make certain that the selector is set to the vertical, semi-auto position before disassembly and do not reposition it until after the AC-556 is reassembled. Failing to do so almost guarantees that the “rocker arm assembly (MA12600)” and “link positioner assembly (MA12700)” will be damaged. The Ruger AC-556 manual describes the gas system as being, “self-cleaning with 5.56mm NATO ammo.” For that reason, the operating manual does not describe how to disassemble or clean the gas system. After fieldstripping the AC-556 per

the owner’s manual, use the following instructions to clean the gas system. Refer to the picture on page 5 of the owner’s manual as it clearly shows the parts of the gas system. Use a 9/64 (0.140) inch Allen wrench to remove the four cap-screws that clamp the top and bottom halves of the gas block (MS03500) to the barrel. Watch carefully as the lower half is removed from the barrel as the small gas port bushing (MS02500) could fall out. If it stays in its recess, gently pull it out. After it is removed, the gas piston (MS03600) will slide out of the lower half of the gas block. Using only finger power to turn it, clean the small gas port bushing with a 1/ 16-inch drill bit. Scrape away the fouling with the bit being very careful not to enlarge the orifice.

The gas piston has two orifices. Clean the smaller one with the 1/16 inch drill bit. Clean the larger one with a 1/8-inch drill bit. Again, use finger power only. Just scrape out the fouling. The gas port in the barrel is smaller than 1/16-inch. Use an open paper clip to clean it. Reassemble the gas system. Avoid over-tightening the cap screws. The threads can be stripped. Run a cleaning rod with a patch through the barrel to remove any fouling that was pushed into the barrel while cleaning the gas port. Clean the chamber as previously described. Finish reassembly per the owner manual instructions. Before replacing the trigger group, be certain that the selector is set vertically to semi-auto. Also make certain that the vertical arm of the “link positioner assem-

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bly” is straight up as well. Shooting an AC-556 The rear sight of an AC-556 is an aperture that is adjustable for both windage and elevation. Unlike an M16 rear sight though, an AC-556 rear sight is not a quickly adjustable flip-over “L” that is zeroed for two distances. Given the flat shooting trajectory of the 5.56mm NATO round, a two-position rear sight is unnecessary. If an AC-556 rear sight is adjusted so that the bullet hits dead-center at 300

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yards (274 meters), the bullet’s trajectory will not be more than 5 inches (12.7 cm) above or below the line of sight between the muzzle and 350 yards (320 meters). For most users of an AC-556, this is quite sufficient. Like an M16, an AC-556 is a lightweight full-auto firearm. Neither one is particularly controllable in full-auto. Both have light-weight air-cooled barrels as well. More than one RKI has reported that firing three consecutive 30-round bursts in either firearm will permanently diminish its accuracy and make the barrel so hot that

if a round is left in the chamber, it will “cook off” in ninety seconds. For these reasons, sustained full-auto fire is not recommended in either. Firing several consecutive 30-round bursts of .22LR ammo will leave lead deposits in the barrel but the heat that is generated is not sufficient to damage it. The author has never heard a report of a .22LR cartridge “cooking off” in either an AC556 or in an M16. Safety minded shooters will not tempt fate though by leaving an unfired round in the chamber of either after firing multiple long bursts.

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Ruger AC-556 or Colt M16? Which full-auto firearm will best suit a SAR reader’s needs, a Ruger AC-556 or a Colt M16? An AC-556 has three minor advantages over an M16 and one major one. If long exposure to saltwater or lower cost is a requirement, the obvious choice is the Ruger AC-556. Stainless steel KAC-556s are not rare and an AC-556 is generally priced at one-half to one-third of the cost of a Colt M16. Except for a very few Group Industries stainless steel M16 receivers, stainless steel is not an option for an M16. For most users however, stainless steel is unnecessary. Third, the AC-556 gas system does not blow unburned powder and other residue of combustion into critical places in the receiver. Due to the nature of the M16 gas system, it will become dirtier faster than an AC-556. An AC-556 will function longer without cleaning than a M16. However, for non-military use, fouling accumulation is seldom a problem. Fourth, and a very useful feature, unlike most machine guns, the AC-556 is not readily identifiable as a machine gun. The differences between an AC-556 and a Mini-14 are subtle. Both lack a prominent pistol grip and neither look like the news media’s idea of a dreaded “assault rifle.” This is particularly true if an optical sight is installed. An AC-556 is a wise choice of firearm if stealth is a requirement. An AC-556 may be carried, without undue attention, anywhere that a hunting rifle may be taken. Regarding accuracy, as they arrive inthe-box, neither a Colt M16 nor a Ruger AC-556 is a tack driver. Much more developmental work has been done on the M16/AR-15 though than on the AC-556 to enhance accuracy. It would be much easier to turn an M16 into a minute-ofangle rifle than would an AC-556. The only practical caliber conversion that can be made to a Ruger AC-556 is to .22LR. A reliable .22LR kit is available for the Colt M16 as well. Due to the M16’s easily removable upper receiver though, many other practical caliber conversions are available for it. These include 7.62x39mm, 9mm Parabellum, .45ACP and .50 Action Express. Of the two fullauto guns, the M16 is the most versatile. Other practical considerations are

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the M16 has no advantage over the AC556. An AC-556 is the cost-effective choice. A reliable .22LR converted AC-556 is a near ideal firearm to use when introducing novices to full-auto fun. The ammo is cheap, there is virtually no recoil and the sound of the shot is not intimidating. It is pretty much guaranteed that smiles and excitement will be generated when newcomers are exposed to this full-auto fun and is sufficient reason to own a Ruger AC556.

spare parts and accessories. Virtually no spare parts or accessories, other than optical sight mounts and magazines, are available for a Ruger AC-556. As for the Colt, few firearms have as many spare parts and drop-in accessories available to them as do M16s and AR-15s. The RKIs’ general consensus of opinion is this, “The Ruger AC-556 is a rifle. The M16/AR-15 is a system.” The Author’s Opinion There are many good reasons to own a Ruger AC-556. Simply not owning one

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was a good enough reason in the beginning for me to buy one. I rationalized that there was an empty space in my gun vault. There are more practical reasons though to buy an AC-556. At one-third to one-half the cost of an M16, an AC-556 is more affordable. The AC-556 is available in stainless steel. With Ruger and certain other magazines, it functions flawlessly. An AC-556 can pass for a sporting rifle and there is a reliable .22LR kit for it. The Ruger factory will fix an unaltered AC-556 if repairs are needed. Unless the potential owner needs the option of quick centerfire caliber changes,

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Sources

Dial Calipers Dillon Precision Products, Inc. 8009 E. Dillon’s Way Scottsdale, AZ 85260 480-948-8009

.22LR Conversion Kits Jonathon A. Ceiner, Inc. 8700 Commerce St., Dept SAR Cape Canaveral, FL 32920 321-868-2200