Early this year (2010), I wrote a short note on “AK doubling” for the Italian web site exordinanza.net. Some days later, a guy from a friend's site wrote that ninety per cent of the times this malfunction occurs a slam fire is the culprit. He did not know what he was writing about. The so called "slam fire" is an extremely dangerous malfunction that takes place when the firing pin for some reason is sticking in the bolt in a protruding position. When the bolt slams forward, the gun fires in a more or less unlocked condition. It may also happen in combination with a heavy firing pin, the absence of a firing pin spring and a sensitive primer.

There is another unusual cause: a cratered primer of a previously fired round may project small metal fragments into the firing pin hole that acts as a wedge blocking the firing pin forward. I have seen an SVD from China blown up such way. In this case, an over dimensioned firing pin hole and poor quality factory ammunition from an Eastern country producing cratered cases were to blame.

Anyway, doubling is a horse of another color. Technical manual Army TM 9- 1005-249-23&P for M16 rifle at paragraph .13 of page 3.9 (Chapter 3 Section III: Troubleshooting) writes: “(weapon) fires when trigger is released with selector lever on semi-auto, or fires two or more rounds in semi selector position (Doubling)." Thus, we learn that the problem has two distinct points: (1) the weapon fires when the trigger is released, (2) the weapon fires two or more rounds in semi-auto mode. Let's first take into consideration point (2), which is more common. The above said Manual at Step 1 of paragraph 13. page 3.9 indicates “defective disconnector” as a cause of the malfunction and “Replace the disconnector” as corrective action.

Now we return to our AK doubling problem. The firing mechanism of the M16 is partly similar to that of AK rifles, which suggests the use of good old U.S. Manuals. Moreover, the AK has another helpful characteristic: after removing the bolt cover, the firing mechanism can be observed with ease. Thus, the cause-effect relationship of what happens can be positively understood.

I think that the doubling malfunction tests of an AK should be conducted beginning from the point (1) of above, i.e. when weapon fires two or more rounds in semi-auto position. With the trigger held to the rear after charging the weapon, we note that the hammer is retained by the disconnector. With a fingertip, exert a moderate pressure both ways on the disconnector. If the hammer falls this means an insufficient grasp of the disconnector on the hammer. An insufficient grasp can be cured by cautiously filing the forward side of the disconnector in order to make it advance and get a wider contact surface. If you have at hand a supply of spare parts, perhaps a new disconnector is a better solution. Sometimes the problem lies in a weak or defective disconnector spring, so replacing it to obtain a stronger grasp is a good idea. On the other side, a stronger disconnector spring will increase that trigger slap, which seems to bother some shooters. In most cases, these changes will solve the problem. Vibrations from firing will not jar the hammer free if the disconnector works properly.

I noted that my Chinese Norinco Model 84S in 5,56mm caliber, is more prone to doubling with heavy loads using a fast burning powder. Moderate loads with a slower burning powder reduce the doubling nightmare. With Vithtavuori N140 there is less slam banging and, I think, the cycling of the weapon is slower.

If disconnector is okay, we have to test according to point (1) of above, that is, a weapon that fires when the trigger is released. With the bolt cover off and the trigger held to the rear, charge the weapon and release trigger with a slow and smooth motion. Repeat the operation five times. If the hammer falls in any of these five tests we are facing a typical timing problem of Chinese M84S rifles. Testing my Norinco M84S, I noted that releasing the trigger, the primary sear that is integral with the trigger does not come up fast enough to intercept the hammer. That is why the hammer falls and the weapon doubles. A stronger trigger spring could be the cure.

How dangerous is doubling? Nobody can say at what phase of locking the doubling takes place, so it is reasonable to say that it may be very dangerous with risk of injury to the shooter. Firing my Norinco M84S with near maximum loads of a faster burning powder resulted in cases with shortened necks and advanced shoulders.

When Norinco introduced the Model 84, they demonstrated a low sense of responsibility. To make the full-auto AK legal for the civilian market they simply discarded the automatic sear and pin to render automatic fire impossible, ignoring the fact that in the AK design the automatic sear wears also functions as a safety sear by impeding the hammer fall until the bolt carrier has completed locking the bolt. Norinco failed to add a serious mechanical safety of a new type that permitted firing only in a fully locked condition.

Finally, there is only one more thing to say on the matter. Many years ago I red in the American Rifleman (Q&A section) that a shooter capable of controlling his finger movement to the point of stopping the pressure on the trigger as soon as the hammer falls, will produce more doublings than a poor shot who jerks the trigger. The reason lies in the fact that stopping the finger movement may cause an incomplete engagement of the hammer on the disconnector, thus producing doubling. In this case, there is no remedy because up to now you cannot mail order a spare human brain.

ADDENDUM

Further study and observations enable to give now a definite answer to a point left dubious in my article on Chinese Semi-automatic AK Rifle Safety. It's the case of a weapon that fires (doubles) when trigger is released. I was right in hypothesizing that the trigger, integral with the primary sear, does not come up fast enough to intercept the hammer. However, the cure I suggested at the time (a stronger hammer spring) wasn't a big help.

Attentive examination of an Izhmash Saiga 308 Win., two pin model made for the hunting market revealed that the real problem was elsewhere. In the well made Russian rifle it was noted that, with trigger pulled and hammer retained by the disconnector, the distance between the sear surface of the trigger hook and the engagement area on the hammer is kept to a minimum, about 0.3 to 0.4 mm. When the trigger is released, the disconnector rotates to the rear allowing the hammer to fall, but the trigger hook, being so close, has the right timing to intercept it. The shorter the trigger hook travel, the quicker its operation.

In many AK rifles, including my Norinco 84S, tolerances are looser, so the rifles double. What can be done? My remedy was similar to that of Swiss gunsmiths when they sought to improve the trigger pull of Model 1924 and Model 1929 military Luger pistols for target shooting: get a box full of L-sear levers and search for the right one.

I was lucky. At the second attempt, from an assortment of triggers and hammers coming from every country of the former Eastern Bloc, I found the combination that gave the proper timing. Probably for American shooters it's better to order one of the many American made AK trigger groups. They have a lot of advantages and one minor disadvantage: they are not cheap as Bulgarian parts.