How to Check Feed Lip Width on Standard-Issue Magazines

As we mentioned in last week’s Force Mod/Fossil Friday post, there is a new Magazine Feed Lip Wear tool available for the standard-issue magazines for the M4A1. However, what are we to do if we don’t have access to it?

For Walkthrough Wednesday, we answer that question. All it takes is the use of a digital caliper capable of detecting to the thousandth of an inch. To ensure our feed lips are set at the proper distance apart from each other, we press down on the follower (the plastic portion of the magazine that the bullets rest on) and then check the gap between them. The dimensions of the permissible gap between the feed lips is .4480 to .4760 inches.

Using the caliper instead of the feed lip wear tool takes a little longer, and requires you to check in multiple places from the front edge to the back edge. The best practice for the standard-issue magazines with the coyote tan follower would be to write down these results and average them out for a specific magazine. Once that is done, ensure it fits in the permissible gap. Inexpensive digital calipers can be purchased at places like Lowe’s, Home Depot, Harbor Freight, etc. And can be used for various other things (e.g. determining group size at 25 meters). While this method is more time consuming than the feed lip wear tool, it is an alternate method that can be used for the standard-issue magazines.

One thing of note; the Enhanced Performance Magazines (coyote tan with a blue follower) have a slight taper to the feed lips. The width should go from wide to narrow as you move from the ‘back’ of the magazine towards the ‘front’ (from where the rim of the case rests to where the nose of the projectile is). As long as the magazine is within the permissible gap, the magazine is good. Ideally, the low end of the gap would be at the front (projectile) edge of the magazine (.4480) with the widest part being at the back (primer) edge of the feed lips (.4760).

Long story short; check your magazines, ideally use the feed lip wear tool, but if one is not available, you can use this alternate method. If the magazine is out of spec, turn them in in a fashion that guarantees they will not be reissued, and get a new magazine. Do this check at least once a month as a part of Preventive Maintenance Checks and Services, and number your magazines with a paint marker to ensure you know which one is which.  Leaders need to understand that it is the magazine that causes more malfunctions than any other part on the weapon. The magazine is also the part least likely to get any form of maintenance.  Ensuring our Paratroopers conduct PMCS of their magazines will reduce the malfunction rate with the M4A1.

#weaponsmastery #getridofbadmagazines

Raymond Miller
82nd Airborne Division Small Arms Master Gunner: primary weapons trainer, force modernization for individual weapons, and range liason for the 82nd.


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