I've read Armalites reasoning that they posted some time back about why Armalite didn't go with FAL mags
FAL mags don't really have feed lips.
The reason they chose M14 pattern is because the rifle came back during the AWB; M14 mags are cheap, plentiful and easily modified to fit the AR-10 (seriously: A hammer, small chisel, Dremel and 15 minutes is all that's needed). There was a huge supply of 20 round mags available this way, so people could have the standard capacity mags during those dark years.
Honestly, it's kind of a mystery why DPMS and the others didn't go with the Armalite modified M14 pattern. The gen I mags had some issues due to the BHO catch dragging on the mag body under spring pressure, but the Gen II mags are basically just scaled up AR-15 mags and run flawlessly.
ETA
Here's the article:
Industry » ArmaLite » FAQ; Why ArmaLite doesn't use the FAL magazine (Page 1)
0 ArmaLite :: 1/13/2006 6:02:35 PM EST
We've published this FAQ several times over the past decade as customers ask why we don't use a cheaper magazine. Here's an update based on the latest inquiry.
Q: Why doesn’t the AR-10 use FAL Magazines? They’re cheap.
A: The FAL magazine suffers from technical weaknesses when applied to the AR-10.
Normally, a rifle magazine should be built to suit the rifle mechanism instead of the rifle mechanism being built to match the magazine. At the time the AR-10 was designed, however, the Assault Weapon Ban was in effect and ArmaLite could not produce new magazines for commercial customers. If 20 round magazines were to be available to its customers, ArmaLite needed to use a magazine that was already in existence and could be used intact, or with slight changes. Four magazines were considered:
M-14 (which was derived from an earlier government test magazine)
G-3
Early ArmaLite AR-10 magazine
FAL
The G-3 and early AR-10 magazines weren’t easily available at the time, so were written off early. The logical choices came down to either the plentiful M-14 or FAL magazines.
Mark Westrom was attracted to the low price and easy availability of the FAL magazine, and studied it and others thoroughly. The FAL magazine is very effective in FAL rifles. Unfortunately, it suffers a number of characteristics which make it very much less suitable for use in an AR-10.
The FAL magazine is not a stand-alone feed device. It merely contains cartridges and presents them to the feed lips in the rifle. The actual, functional feed lips are machined into the upper receiver. The feed lips protect the magazine’s lips from damage. The machined lips are in close alignment with the chamber and tolerate poor quality magazines. Because the AR-10 requires the magazine lips to feed, the FAL magazine was not determined to be tough enough for an AR-10.
Next, studying of the movement of the cartridge during feeding revealed that the M-14 magazine closely matched feeding from the early ArmaLite 10 magazines, and was thus very suitable to feeding up the barrel extension of the AR-10.
The feed from a FAL magazine was very much different and obviously required dramatically ramping the bottom of the barrel extension in a way that cut deeply into the lowest locking lug. This reduces not only the strength of the barrel extension, but the symmetry with which it accepts recoil loads from the bolt. The M-14 magazine thus allows a stronger action in the AR-10 than use of a FAL magazine would.
Unless modified by cutting an M16 style magazine catch slot in it, using the FAL magazine requires the action of the rifle to be built considerably longer than the action of the AR-10. The magazine itself is longer, and the magazine locking and bolt catch mechanisms behind it required more space between the trigger pocket and the barrel. The whole action thus must be longer, as well as the carrier. Both weight and length are increased.
ArmaLite was not alone in declining to use the FAL magazine. Two other firms building .308 caliber rifles settled on another magazine design. One of them put considerable effort into trying to use the inexpensive FAL magazine, but found that even an adjustable magazine catch made the proposition a failure. In the final analysis, ArmaLite accepted the tough, proven M-14 magazine as the basis for its AR-10 magazine. A third firm actually fielded a 7.62mm rifle with the FAL mag and it was a miserable failure, although it was difficult to tell if it was because of the mag or general incompetence. A fourth firm tried to introduce a rifle with a FAL mag and has failed to date, with considerable delay in introduction.
Three other companies did try the FAL magazine. All experienced significant problems with feeding and those rifles are now apparently off the market.
In the final analysis, it is poor policy to accept a magazine only because it is cheap. It’s letting the tail wag the dog, and if the rifle proved popular the supply of inexpensive magazines would disappear, prices would rise, and the advantage would be lost anyway.
ArmaLite will therefore not alter its design by switching from the proven M-14 magazine technology.
