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Trouble Shooting
I have compiled a small troubleshooting guide below that address some of the most common issues. Click on a issue for a short description and fix.
My M-11 is a Jamomatic
My full-auto M-11 only shoots one round at a time or only burst
My full-auto M-11 won’t stop shooting when I let off the trigger
My semi-auto M-11 is painful to shoot
My M-11 doesn’t hit where I aim it


Before going into the reasons for malfunctions, you need to know how to safely clear a jam in your open bolt SMG, which you'll find is different than most of your pistols.

Think "B-B" (Bolt Back)!    Do NOT take the magazine out of the gun until you have locked the bolt back (if you can), otherwise it may go forward on a live round when the mag is released and discharge. Lock the bolt back and put the gun on SAFE and THEN remove the magazine. If you can not lock the bolt back, at least control the bolt in the rearward position by holding the bolt knob as you remove the magazine. You can then clear the chamber and also make sure that the bore/barrel is clear. ALWAYS keep your gun pointed in a safe direction downrange!
My M-11 is a Jamomatic
If your M-11 is jamming, the most likely cause is the magazine, especially with M-11s using Zytel magazines since these can split easily or have worn feedlips. Check your magazine, and if any problems are found, replace or repair the magazine.

Check out the Zytel Magazine Repair section on the menu to the left for tips on repairing your Zytel magazine., and the Magazine Overview page for alternatives to the Zytels.

Also, many M-11s dislike Hollow Point (HP) or Flat Point (FP) ammunition because the nose of the bullet can get caught on the feed ramp. Try using Round Nose (RN) plated or Full Metal Jacket (FMJ) instead.

A. Normal

B. Abnormal – most likely a worn out magazine spring

C. Abnormal – most likely worn / split feed lips

It's also possible that even with "good" magazines like the new metal ZMags from Shockwave Technologies, you might need to have your feed ramp adjusted. This can (and should) be done by a gunsmith familiar with the MAC platform (see the "links" page), but if you're feeling industrious and want to try it yourself, here is the procedure courtesy of Richard Lage at Lage Manufacturing:

You can adjust the feedramp up to eliminate the bullet tips jamming on the barrel edge. To do this, remove the fire control parts and place a couple of layers of tape on the feedramp to protect it. Place an adjustable wrench on the feedramp and close the jaws down on it. Pry up a little and then check the height by placing the upper on the lower without the bolt assembly installed. Place your "pinky" finger in the ejection port and slide it up the feedramp and into the barrel chamber. You should feel a smooth transition. If it is not, use the adjustable wrench again to move it until it is.

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My full-auto M-11 only shoots one round at a time or only burst

There are a number of reasons why your M-11 may be doing this.

A. Worn Sear – Very Common
B. Worn Trigger Spring – Not Common
C. Worn Disconnector Roll Pin – Not Common
D. Worn / Malformed Trigger Frame – RARE
E. Malformed Receiver - RARE

Worn Sear
This is the most common reason that your gun is shooting only in burst. The area where the disconnector engages the sear is worn and the disconnector is “disconnecting” to early. Most common cause for a worn sear is the part was not heat-treated properly.

To fix this you must purchase a new sear.

A. Area marked in green is location where the wear would be located.

Worn Trigger Spring
This is not a common problem, but it does happen from time to time. A worn trigger spring is usually the result of it being bent or damaged during installation. Also the spring may have taken a “set” if the gun remained unused for a very long time.

To fix this you must purchase a new trigger spring.

Spring pictured is what a normal one should look like.

Worn Disconnector Roll Pin
This is not a common problem, but it does happen from time to time. A worn disconnector roll pin is usually the result of it being bent or damaged during installation, normal wear and tear in “high mileage” guns (lots of rounds and the part just wore out), or some part of the gun struck the disconnector too hard (as a result of a ammo problem).

To fix this you must purchase a new role pin.

A. Area marked in green is where the roll pin is located.

Worn / Malformed Trigger Frame
A worn trigger frame rarely occurs and is usually a result of a poor heat-treated part or a catastrophic ammo failure in the gun.

Two problems can occur to the trigger frame. The first is that the area in which the disconnector resides, colored purple, can become bent or malformed resulting in a disconnector that doesn’t sit straight or is stuck. The most likely cause is that the trigger frame was poorly heat-treated.

To fix this you can either bend the two “ears” back into position so the disconnector doesn’t wobble and sits straight, or you can just purchase a new trigger frame.

The second problem is the result of a catastrophic ammo failure. The trigger frame’s axis pinholes, colored green, have “stretched” out from excessive force. The trigger now sits awkwardly in the gun misaligning the disconnector.

To fix this you will need to purchase a new trigger frame.

Parts pictured to the right are how a normal trigger frame should look.

Malformed Receiver
This is a really rare problem caused by poor factory frame welds on the receiver or a catastrophic ammo failure. Basically the receiver has become bent or malformed misaligning the entire FCG. Shooting a gun in this condition is dangerous.

If you are not sure that your gun has this problem send it to a gunsmith to have it looked at.

The only way to fix this is to send it to a “MAC smith” to have the receiver straighten out and re-welded.

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My full-auto M-11 won’t stop shooting when I let off the trigger
This is a very dangerous condition and can result in some one getting hurt, so if this occurs on your gun get it fixed ASAP!

The most common cause is a worn sear face, colored in green, and or worn sear catch on the bolt face, colored in purple. Basically the bolt slips off the sear which is supposed to hold it back when the trigger is released. This condition is usually a result of the parts being poorly heat-treated.

There are two ways to fix this.

1. You can attempt to clean up the worn areas with a file and reform them so they are no longer “rounded”. This is not recommend because it doesn’t solve the initial problem of the parts themselves being poorly heat-treated.
2. Purchase a new bolt & sear.

Another cause, though uncommon, is the ammo itself. If the ammo is underpowered it might just push the bolt back far enough to cycle again but not engage the sear. This occurs most often with improper reloads.

To fix the underpowered ammo problem purchase some decent ammunition.

A. Sear Catch on Bolt Face
B. Sear Face on Sear

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My semi-auto M-11 is painful to shoot

That pain in your trigger finger is called “trigger slap” and is a common occurrence with semi-auto M-11s. “Trigger slap” is caused when the bolt recoils back forcing the hammer down until it engages the sear plate. As the hammer engages the sear plate the sear over travels and then moves the trigger frame forward. This over travel “slaps” the shooters finger causing pain.

This trigger slap is the result of a flaw in the design of the semi-auto M-11 fire control group. There are no true fixes, but you can reduce its effect.

Several ways to reduce the M-11’s trigger slap

1. Polish hammer engagement surface on the sear plate. Go slow and make sure that the hammer can still be engaged by the sear when you are finished or the gun won’t run correctly. I don’t recommend this because if you remove to much material you can mess up your FCG.
2. Install a piece of rubber hose on the trigger. Most guns from the factory all ready have a piece of rubber hose on the trigger. If yours does not it might be a good idea to add one. The rubber hose acts as a cushion between your finger and trigger absorbing some of the slap.
3. Change shooting technique. Shoot with the tip of your trigger finger and quickly remove it after every shot. Don’t wrap your trigger finger completely around the trigger.

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My M-11 doesn't hit where I aim it

As far as the original sights are concerned, you look through the little hole in the backplate or the U-shaped slot (your gun may have one or both of those depending on the year of manufacture) and line up the front sight, which is a little "finger" of sheet metal between two protective ears. If your point of impact is way off from your point of aim, you can adjust the sights on the gun by carefully bending the front sight up, down, left or right, as needed. For example, if your gun shoots low, bend the front sight down slightly so that it brings the muzzle up when you're aiming. You probably won't have to bend it much to get the correction that you need, and be careful not to break the front sight since they can get brittle as they get old. That's never happened to me in the several Macs that I've adjusted, but still, it might be a good idea to heat it slighly with a propane torch before you attempt to bend it much. If your front sight *did* happen to break off, it can be spot welded back together by a competent gunsmith.

If you have a backplate with both a hole and a U-cutout notch like the version shown in the photo here, you can alternate between them to adjust elevation for different distances. You can also easily cut a notch like that if your backplate only has the hole... I did that to one of my M11 guns using a Dremel cutting wheel and using some cold blue on the exposed metal in the slot, and now it looks and functions just like my other M11 that came that way from the SWD factory.

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