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Posted: 8/3/2007 7:56:23 PM EDT
| Why are MP5 9mm mags curved when virtually every other 9mm SMG, Colt, Uzi, Mac, Sten, S&W 76, German MP40, etc. are all straight. Heck even all the other H&K SMG mags are straight, just not the MP5 9mm. What is the deal? |
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9mm is a tapered round. While it is obviously possible to stack 9mm in a straight magazine, the cartridge is not ideally suited for use in them. There is an increased risk of cartridges nosediving in a straight magazine because the narrower front of the cartridge isn't as positively supported as the wider rear of the cartridge. A curved magazine allows the tapered rounds to stack naturally so that they are properly supported along their full length. This helps prevent differences in the presentation of the cartridge. When trying to feed 9mm in a straight magazine, there is an increased risk that the cartridge will be presented at different angles. This is particularly noticeable with Uzi magazines. When an Uzi magazine is nearly empty the cartridges tend to conform to the angle of the follower. When the magazines are full the cartridges tend to conform to the angle of the feedlips. The feedlips on Uzi magazines even have an upward sweep to them near the front to account for that. Round-nose ammunition has a relatively easy time feeding because the round nose acts almost as its own feed ramp, making it fairly forgiving of minor misalignment. Hollowpoints on the other hand effectively have a blunt nose which can catch on surfaces a round nose would glide over. There's a reason HK MP5 magazines are straight in calibers other than 9mm. The .40S&W, 10mm, and .45Auto cartridges are either non-tapered, or only a couple of thousandths away from being non-tapered. Such straight cartridges can easily be stacked in a straight magazine and still offer full support of each cartridge. Making curved magazines for those cartridges would be more difficult and actually make the feeding less reliable because the rear of the cartridges would not be positively supported. Straight magazines were never ideal for 9mm, but considering that most 9mm SMG's--particularly WWII era SMG's--were designed with only round-nosed ammunition in mind, straight magazines were good enough. |
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The original MP5 mags were straight. I'm not sure when they changed to curved...early '70s IIRC. Another option for tapered ammo would be a wedge shaped magazine like the Czech Cz24 subguns. The mag is slightly less than 2 catridges wide at the rear & angled to be slightly more than 1 cartridge wide at the front. Pix here Czech mag Re Sterling mags. Will they work in a 9mm AR? Not as cheap or easy to find as Uzi mags but if they're among the best smg mags made it might be worth checking out modding a mag well adapter to use them. |
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Sort of building on Golovko and RiffRandall's points, it appears to me that the straight Sten magazine is engineered to discourage nose diving. This may be a moot point, as the Sten magazine is a single feed, so I apologize if my observations serve no purpose here. Similar to the Czech subgun magazine the Sten magazine is tapered, being narrower in the front and wider in the rear. To encourage proper feeding, the Sten magazine follower is pitched upwards at the front of the magazine. The magazine is also longer (front to back) than the 9X19 round, presumably allowing for the rounds to remain seated at the nose-up pitch. Lastly, the lips on the Sten magazine flare open slightly towards the front of the magazine, further encouragining the nose-up position and assuring a good feed. Sort of hard to see, but there is a cosiderable gap between the magazine wall and the front of the round. http://i22.photobucket.com/albums/b349/_hikeeba_/Gun%20stuff/StenLoader03.jpg Nose-up position of round in a loaded magazine. http://i22.photobucket.com/albums/b349/_hikeeba_/Gun%20stuff/StenMag.jpg |
I tinkered with some Sterling mags with the Oly 9mm and could'nt get it to work RELIABLY. When it did work, it was like butter...but most of the time, nada. If I had access to some better machine tools than my dremel, who knows. It might have an easier time in a Colt type system. One of the major problems is the original Sten setup is a single position feed while the sterling is double. Try it out, I'd love a block for the Sterling...great mags...and I've got a bunch. ka |
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