In another thread, the 30-round magazine was brought up and I thought now was as good a time as any to give a brief run-down on its development.
Initially the Army bought the M16 (XM16) with the simple 20-round magazine, and since that was what the M14 and T48 used, no further thought was given to the matter. Then in 1965, the Small Arms Weapons System evaluation was started with several weapons systems being evaluated. These were the M14/M60 combination, the Stoner 63 Weapons System, the AK-47/RPD/DPM combination, and Colt's M16A1 and Colt Automatic Rifle, basically, a heavy, removable barrel AR-15.
The Stoner 63, the AK and the Colt AR all used a 30-round magazine, and some of the evaluators started to think that a 30-round magazine in the M16 wasn't that bad an idea. But at the time there was no military requirement for a 30-round magazine, but if there ever where such a requirement in the future, the Colt AR magazine might be a good choice.
Increased usage of the M16 in combat in Vietnam resulted in a requirement for the 30-round magazine in mid to late 1966.
The Colt AR's 30-round magazine is a uniform curve magazine, very similar in profile to the Stoner 63 30 round magazine. It was thought that because the lower receiver of the Colt AR was the same as the M16 lower it would be a simple matter of inserting the Colt AR magazine in the M16. But things are never simple. Due to a wide variation of tolerance on the length of the M16's magazine well, some would indeed fit and work, but some would take a slight nose down attitude and snub rounds on the rear face of the barrel extension, and others just wouldn't fit. So the magazine was redesigned with a straight upper half and an increased curve on the lower half of the magazine, the profile we know today. In mid-1967 a prototype batch of the new profile 30-round magazines was tested in the M16 and CAR-15 (XM177), and found acceptable. A year later, a small pre-production lot of the new magazines was tested and the results were the same as the prototypes. Production started as soon as funding was available, but it wouldn't be until 1969 or 70 that the new 30-round magazine was commonly available.
In Vietnam, the XM177 is the M16 variant most commonly seen with the 30-round magazine as, I believe they were shipped with these. The 20-rounders remained in service until attrition and rotation of weapons out of service eventually saw the 20-round magazine phased out of service.
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The 30-round magazine is actually quite different from the 20-round magazine in terms of construction. The 20-rounders are made from a single piece of sheet aluminum folded to form the box and spot welded along the back, with a strip of sheet steel riveted to the front to prevent the bullets from denting the front wall under recoil. The front strip was found to be unnecessary, and the new design had right and left halves spot welded on both the front and back. There are also slight changes to the lip geometry, and the follower material was changed from cast aluminum to Nylon 6/6.
By the mid-1990s, with the introduction of the M4, the magazine when through another round of changes, all relating to the follower, first the green follower, then in the 2000s, the tan follower, both intended to reduce "follower-tilt" malfunctions. With the introduction of the M855A1 and the Marines' M27, further modifications were required to the lips to bring the nose of the bullet up and pointed more at the chamber. These were required due the exposed steel nose of the M855A1 hitting and scarring the aluminum portion of the feed ramp, and the fact the the rear face of the M27 barrel is flat, rather that the shallow cone of the M16 series.
The USMC seems to have opted out of this last change, preferring to go with Magpul Industries' PMAG M3. This actually marks the first standardized use of an all-plastic (save the spring) magazine in the US Military.
Initially the Army bought the M16 (XM16) with the simple 20-round magazine, and since that was what the M14 and T48 used, no further thought was given to the matter. Then in 1965, the Small Arms Weapons System evaluation was started with several weapons systems being evaluated. These were the M14/M60 combination, the Stoner 63 Weapons System, the AK-47/RPD/DPM combination, and Colt's M16A1 and Colt Automatic Rifle, basically, a heavy, removable barrel AR-15.
The Stoner 63, the AK and the Colt AR all used a 30-round magazine, and some of the evaluators started to think that a 30-round magazine in the M16 wasn't that bad an idea. But at the time there was no military requirement for a 30-round magazine, but if there ever where such a requirement in the future, the Colt AR magazine might be a good choice.
Increased usage of the M16 in combat in Vietnam resulted in a requirement for the 30-round magazine in mid to late 1966.
The Colt AR's 30-round magazine is a uniform curve magazine, very similar in profile to the Stoner 63 30 round magazine. It was thought that because the lower receiver of the Colt AR was the same as the M16 lower it would be a simple matter of inserting the Colt AR magazine in the M16. But things are never simple. Due to a wide variation of tolerance on the length of the M16's magazine well, some would indeed fit and work, but some would take a slight nose down attitude and snub rounds on the rear face of the barrel extension, and others just wouldn't fit. So the magazine was redesigned with a straight upper half and an increased curve on the lower half of the magazine, the profile we know today. In mid-1967 a prototype batch of the new profile 30-round magazines was tested in the M16 and CAR-15 (XM177), and found acceptable. A year later, a small pre-production lot of the new magazines was tested and the results were the same as the prototypes. Production started as soon as funding was available, but it wouldn't be until 1969 or 70 that the new 30-round magazine was commonly available.
In Vietnam, the XM177 is the M16 variant most commonly seen with the 30-round magazine as, I believe they were shipped with these. The 20-rounders remained in service until attrition and rotation of weapons out of service eventually saw the 20-round magazine phased out of service.
The 30-round magazine is actually quite different from the 20-round magazine in terms of construction. The 20-rounders are made from a single piece of sheet aluminum folded to form the box and spot welded along the back, with a strip of sheet steel riveted to the front to prevent the bullets from denting the front wall under recoil. The front strip was found to be unnecessary, and the new design had right and left halves spot welded on both the front and back. There are also slight changes to the lip geometry, and the follower material was changed from cast aluminum to Nylon 6/6.
By the mid-1990s, with the introduction of the M4, the magazine when through another round of changes, all relating to the follower, first the green follower, then in the 2000s, the tan follower, both intended to reduce "follower-tilt" malfunctions. With the introduction of the M855A1 and the Marines' M27, further modifications were required to the lips to bring the nose of the bullet up and pointed more at the chamber. These were required due the exposed steel nose of the M855A1 hitting and scarring the aluminum portion of the feed ramp, and the fact the the rear face of the M27 barrel is flat, rather that the shallow cone of the M16 series.
The USMC seems to have opted out of this last change, preferring to go with Magpul Industries' PMAG M3. This actually marks the first standardized use of an all-plastic (save the spring) magazine in the US Military.
