Those Who Forget the Past, AR-15 Edition

A couple of days ago we followed a link from The Gun Feed to the Michigan-based gun blog 248 (We’re guessing 248 is an MI area code? The way the Workshop Eating Plane® will have “603” in its N Number?). Anyway, the article was a short and to the point gear review of an extended or enhanced mag release that is made by a company called ArmaSpec.

Armaspec calls it the “Tactical Combat Button,” and says (right there on the package!) that it gives you “faster magazine changes.” It’s reminiscent of popular extended or enhanced mag catches that have become common on sidearms, like the Vickers Tactical catch we have in our Glock 17. (We’ve got the slide release, too. Larry is a hero to those of us with small hands).

Apart from the name, which gnaws at us in its jejune buzzwordiness (not “tactical” again! And “combat?” Whose?), it illustrates the problem of living in Baby Duck World, where All Things Are Ever New™. This button may be useful for someone running very stylized match stages, but it probably isn’t.

Here are our problems with the TCB, conceptually:

  1. First, there’s nothing wrong with the standard mag catch;
  2. Unlike the standard mag catch, this is very prone to unintended mag release;
  3. Unlike the standard mag catch, this cannot be installed, removed or adjusted without tools;
  4. In fact, it needs a peculiar tool which the rubber-meets-the-road system operator may not have on his person;
  5. It gives up most if not all the adjustability of the standard catch;
  6. It introduces additional points of failure into a proven subsystem;
  7. It is vulnerable to the screws backing out and requires Loctite to work at all.

Note that we haven’t tried this part ourselves, we’re just cueing off 248Shooters’ review.

The History of the AR-15 / M16 Mag Catch

The M16 magazine catch started as the AR-15 one, which, of course, began as the AR-10 magazine catch, as shown here. (The first shot is Serial #38, auctioned by James D. Julia some time past; the others are from an Portuguese AR-10 on an H&H Semi receiver). We have not tested the interchangeability of these catches, but we suspect that the AR-10 and -15 catches are the same length on the X Axis (front to rear) but the AR-10 catch is longer on the Y Axis (left to right).


The AR-10 magazine catch was not created in a vacuum. It itself was an improvement of the catch used in the seminal German MP44 assault rifle (We use “MP44” somewhat expansively here; the magazine catch appears to us to be the same in all related versions of the German assault rifle, back to the MKb 42 (H)). The direction of the release changed, and it was moved closer to the pistol grip, so that it could be released with the index finger of the right hand, instead of using the left hand as was done with the MP44. The next photos are of a Japanese non-firing replica of the MP44 (they were the clearest photos handy on the net). The mag release is the conical, ribbed button at the rear of the magazine well.

This next picture shows a weakness of the MP44 system, which the AR system improved materially. As you can see, the catch, button and shaft are joined semi permanently by staking or riveting. That means it’s not field-repairable, let alone, -adjustable, at the -10 or -20 (operator or organizational repair, i.e. unit armorer) echelons. Again, this is a replica, but a very nice one.

By making the AR-10 design a one-piece shaft and catch, where the shaft threaded into a tapped blind hole in the mag-release button, Stoner made it possible for the magazine catch to be disassembled for repair, replacement or adjustment without tools. All you need is a cartridge to overextend the mag release so that the catch clears the magwell, and then it can be screwed in or out. On any AR, a mag catch that’s too “grippy” can be fixed by backing off a couple half turns, and one that’s kind of loose can be tightened up the same way. This adjustment can clear up a lot of “mystery” failures to feed in AR systems.

The magazine catch can’t unscrew itself without being overextended until it’s clear of the magwell, because the magwell holds the catch in place and prevents it from rotating. But as ingenious as the AR-10 magazine catch was, there were still two improvements to come.

The first was to exchange the blind hole of the AR-10 magazine release for a through hole. This made the magazine catch button much easier to manufacture and increased the usable range of adjustment for the magazine catch, with no downsides at all. From this alteration somewhere around 1960, the parts of the standard AR magazine catch are fundamentally unaltered until today. (One change is that the ribbing on the catch is circular, whilst in the early sixties it was straight and horizontal, but this is a cosmetic change driven by production convenience and not material to the function of the catch.

The 17 prototypes made all had a magazine catch that worked much like it has on all the milios of aRs since then. Here is Prototype 004, from the Reed Knight collection:

The initial catch was not guarded at all.

Here it is on the Colt Model 601, the first production AR-15 model, of which approximately 14,500 were manufactured, mostly for military testing (project AGILE, SF/SEAL evaluation in Vietnam, etc.). This catch is identical to those seen on surviving prototypes.

One of the complaints from these early tests was that the exposed magazine release would occasionally lead to an uncommanded ejection of the mag while moving in thick brush.

The Model 602 (which is labeled “Model 02” on the left magwell) was purchased in about 19,000 units, primarily for Air Force base defense and plane/weapons guard purposes. It has the same arrangement of slabside receiver and mag release button. It was with full rate production of the M16 (USAF rifle,  Colt model 604) and XM16E1 (US Army rifle, Colt model 603) that another change to the receiver made it possible to guard or “fence” the magazine release.

The change was the substitution of a captive pivot pin, retained in the lower receiver by a spring-loaded detent running in a groove, much like the rear pin, called the “takedown pin,” had always been. A boss needed to be added to the lower receiver, to provide a race for this pin’s detent and spring to run in. Since the forging dies needed to be modified anyway, it was relatively trivial to extend the boss and make it a “fence” riding above the magazine release.  (This is the center receiver in the three-image picture below). Now, bumping into a stand of bamboo didn’t mean a lost mag any more.

Except, reports from the field indicated that it still did. As a result, the users — mostly the Army, based on Vietnam experience — asked that the rifle be modified, again. The request was brought to the Rifle Technical Committee on 13 Jan 66. It was feasible to change Drawing No. 62300 for the M16 and XM16E1 common lower receiver forging, as the running change log of Product Improvement Modifications records, “To respond to Army request to provide protective boss around the area of the magazine.” The Army contracting office approved the change on 16 May 66, and sometime relatively soon after that date the forging dies were modified to incorporate the “protective boss” which has since come to be known in the collector community as the “full fence.” A comparison of the three different receivers, showing the different forged outer right magwell side, is below, based on thumbnails at the Retro Black Rifle site (which also provided some of the other photos, although the AR-10 photos are from Julia Auctions and from the collection).

Left: prototype through Model 602. Center: Pre-March-66 603/604 (XM16E1/M16). Right: post-3/66 603/604 (XM16E1, from 68 M16A1/M16)

All the earlier forgings were used by Colt; those that were machined already seem to have been used until they ran out on military 603/604s, some were retained for toolroom prototypes and other factory uses, and slabsided, early model forgings with different machining (for a pivot screw instead of a pin) continued to be used on civilian-market semi-auto SP1 rifles for over 20 years.

The fenced mag release solved the problem. It is very rare (a freak occurrence, in fact) to have some stick or branch (or interaction with other gear or aircraft structure, etc.), drop your mag. And yet, there’s no difficulty reaching the mag release with your right index finger and dropping the mag free for a rapid reload. (At least, if you’re right-handed. Yeah, the ergonomics are significantly worse for a southpaw).

Why All this Ancient History Matters w/r/t this Rifle Accessory

The saga of the growing “fence” or boss on the receiver’s magazine well is the story of successive responses to a real problem, inadvertent and uncommanded actuation of the magazine release. You might say the military found that a protected switch was a “tactical” and “combat” necessary, and their users were actually, not Walter Mitty, tactical, and really, not in a practical-shooting-competition stage sense, in actual combat. And they decided a protruding magazine release was a A Bad Thing®. Enough, indeed, of A Bad Thing® that they spent the money not once, but twice, to redo the lower receiving forging to insulate the user against the consequences of a protruding button.

And here’s what the Tactical Combat (gag me!) Button looks like, installed, close-up (this nicely-done image is from 248Shooters’ review, we don’t know if they took it or it’s a factory shot):

As they do note, it’s a well-made small unit, but by installing it, we not only have resurrected the inadvertent mag-drop failure mode, the one that was supposed to be laid to rest in March of ’66, but we’ve also introduced a new failure mode, in that foreign matter can potentially get stuck between the large pad of the TCB and the side of the receiver. In fact, the receiver boss/fence could actually help entrap a vine, stick or other junk right where it keeps you from pressing the mag release down.

This is apart from two of the cons noted by the 248Shooters reviewer, that the screws need to be Loctited, and that, “Like most extended mag releases it does fall pray [sic] to having a bit of wobble.” Against that, we dragged M16 series rifles through Arctic and Alpine conditions in places like Canada, Norway, all over northern New England, and some of the 20k peaks of the Andes, and the factory release is readily manipulated with gloves and even with mittens.

One reason we harp on this design history is that you have to know why the designers designed features into the platform before you go redesigning them, lest you bring back failure modes that engineers thought they banished fifty years ago.

Just like when you hot-rod a car, you may change characteristics that were designed into it for a reason, you need to think before you hot-rod a rifle. If you’ve ever had to drive an undercooled, over-cammed, 12:1 compression race car in traffic, with a did-you-do-your-squats-today clutch and square-cut gears, you know what we’re talking about.


This sort of post is the kind of technical information we most like providing. But the US Department of State has moved to require prior restraint — Censorship, with extremely expensive licensing subject to arbitrary terms — on firearms technical information, in a wild grab to stretch the International Trafficking in Arms Regulations far enough to snuff out freedom of speech. (We’ll have more to say about that soon, including suggestions for how you can help, but from now on until this monstrous and deviant interpretation of the law is put down like a rabid coyote, every technical post will incorporate a note on this subject).

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