The Mac 10 has a reputation as a reliable, if not the most precise submachine gun out there... My experience has been ... well let's just say not that. In fact, statistically speaking, it's my most unreliable firearm. First things first, this gun is cheaply made with cheap materials. However it is simple, so very little can go wrong, and when it does, it's either an easy fix, or the gun is just plain broke. One of the common ailments of the Mac 10 is a phenomenon known (at least commonly referred to) as "trip bounce". This situation manifests itself as full auto on the selector lever, and either only 'burst fire', or interrupted fire or semi auto only fire. The reason for this may become more clear with the image to the right. The "trip" is used to interrupt the bolt movement (prevent full auto in the SEMI setting). A good quick test is to remove this piece from the fire control mechanism and reassemble. It's very easy and almost self explanatory. If the gun works full auto then, you have trip bounce, or a related problem.
Another related problem is 'spring fatigue'. The trigger spring has one end which rests in a recess of the bottom of the frame, right in front of the trigger. The other end holds tension on the trigger "pawl" that pulls down the sear (that's the big thing in the top of the picture). If the spring doesn't hold enough tension, the pawl doesn't pull down fully on the sear, and it leaves the trip loose. A common fix for this is to bend the spring piece toward the front of the gun... Ideally, this would only put more pressure on the pawl and fix the problem. Remember Newton's 3rd law? For every action, there is an equal and opposite reaction ???
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| Mac 10 fire control parts... Nothing complex here. |
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| Click on the center image for a visual on the Mac 10 fire control and some ideas on fixing it.
When the spring is bent forward to compensate for fatigue, a funny, but explainable thing happens, the spring bends underneath the trigger, the spring 'leg' holding the pawl on the trigger "jumps" to the left, the trip jumps up upon recoil and is held in place by the jumped spring leg. You can see the trigger spring wraps around both sides of the trigger. In the picture, the bottom rows have a leg that extends with a short 90 degree bend, that fits into the recess in front of the trigger. This holds the spring in place... Well, kind of...
The upper "leg" of the trigger (upper for the purposes of this picture) extend toward the front of the gun approximately 1 inch. Then, a 90 degree bend toward the "6 o'clock position" in this picture, then that leg that is circled comes up. With the gun apart, after bending that leg forward, everything works fine. That is, until you "load it" by inserting the fire control parts. When you do this, what happens is the 90 degree bend simply slides underneath the trigger (toward the 6 o'clock position in this picture) either totally locking the fire control, or only letting the gun fire semi auto. The leg holding the trigger pawl jumps out and essentially ends the fun. I'm sure there are engineers out there that could figure out in very short order how to design a new spring, modify the fire control, etc. In fact, if they ever see this, they'll probably scoff at my Barrio fix. I say fuck them.
I've heard dozens of people tell me how to bend this spring, so I bought a 6 pack from Cobray. I tried several times with 3 springs, all of which were within 1/10th of an inch on the micrometer before I started. I received the sage advice "make small changes", only bend the spring a little. I tried that (disclaimer: God gave me strong hands, I can break a ceramic coffee mug with either hand, no problem. I'm no surgeon, but I've never injured anyone shaking hands... So I understand and can appreciate the small changes advice....) It only made the spring jump the trip or bind under the trigger.
Funny how all these "keyboard commando" Mac "experts" couldn't produce a working solution. What I needed was 1st hand experience from "A Homey", "'Mano" etc...
You'd be surprised how hard it is to find a banger who's willing to talk... Especially about guns. Anyway, I finally found one by the "alias" Jaime. He clued me in that I needed to weld that spring in place. I popped the Mac Lower out and we discussed it for a bit and came to the conclusion all we needed was to keep that spring from binding underneath the trigger. I thanked Jaime and after thinking about it figured, what the heck? I can fix this with JB weld !  That is, if I had any JB weld  So I improvised; I cut a nail to length, then secured it with Gorilla Glue. Anything is better than nothing... I tested it at the range - I bent the hell out of that spring, installed all the fire control parts and all the play and slop between the trigger / sear is GONE. At the range I dumped 4 magazines, and performed varying length bursts w/o a hitch.
Problem = "solved".
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