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According to the latest info on the midnight movie massacre in Aurora, CO, spree killer James Holmes opened-up on the crowd with a Remington 870. After emptying the shotgun, he switched to a Smith & Wesson AR-15 equipped with a “double-drum” 100-round magazine. At some point during his heinous crime, the mag jammed. Holmes didn’t know how to clear his weapon. So he abandoned the rifle and switched to a Glock .40 caliber pistol. Police aren’t providing a total round count for the entire attack, but there’s no getting around it: the 100-round drum magazine’s failure saved lives. No surprise there. Double-drum magazines suck. Here’s why . . .

1. Double-drum magazines jam  

Most semi-automatic AR-style (a.k.a. “assault”) rifles come equipped with 30-round magazines (except in states which already have a “high capacity” magazine ban, which limit owners to 10-round magazines). It’s a practical limitation. There’s a point after which magazine reliability decreases as the stored round count increases. Dramatically. One hundred rounds is well beyond this practical and literal point of no return.

Even so, aftermarket manufacturers sell 100-round magazines for AR-style rifles. The $179 Surefire magazine is (to my knowledge) the most reliable of the breed. It’s NOT a double-drum-style magazine. Double-drums, as above, are notorious for jamming. Two separate springs have to apply an equal and even amount of pressure at the same time to assure reliable feeding. Introduce other variables—manufacturing errors, temperature fluctuations, gun movement, minor differences in bullet size, etc.—and the cartridges can fail to make it round the horn and into the gun.

It’s only a matter of time before a double drum mag fails, producing one of at least two different problems (e.g., failure to feed and double-feed). While there are ways to address AR-15 magazine failures, there’s no guarantee they’ll work or, if they do, that the shooter will be able to continue shooting unimpeded by another or ongoing mechanical failure. If a criminal wants a reliable way to deliver 100-rounds from a rifle, a double-drum magazine is the worst possible choice. Thank God Holmes chose it.

2. Double-drum magazines limit accuracy  

In the video above, the shooter is firing his double-drum-equipped AR from a seated position with his support arm resting on the bench and his support hand on a fore grip (the handle on the front of the gun). While we don’t see his target, that’s about as good as it gets.

If you’re holding an AR-15 with a double-drum magazine “free hand” (no support) you are holding one heavy gun. One-hundred rounds of .223 ammo (the kind Holmes used in his AR) weighs around three pounds. A Smith & Wesson AR-15 weighs a little under seven pounds. So call it ten pounds total.

While adrenalin makes heavy things seem lighter, accurately aiming a ten pound gun for an extended period of time is no easy task. As the rounds empty, as the gun gets lighter, the handling changes. At the same time double-drums extend the width of the AR, forcing the shooter to “chicken wing” his support arm’s elbow, further reducing accuracy.

We don’t know Holmes’ “hit ratio” but we do know a local gun club turned down his application. If he’d had more experience or chose a better handling AR, one without a double-drum magazine, he would have been more accurate. Perish the thought.

3. Double-drum magazines are hard to conceal

I wish I could say that concealability issues limited John Holmes’ attack. They didn’t. But that doesn’t change the fact that the vast majority of criminals use handguns in gun crimes. Why wouldn’t they? They’re easier to hide. And if handguns are easier to hide than rifles, a rifle equipped with a double-drum magazine is twice as obvious as one without. A rifle with a double-drum magazine would draw more attention than one with a standard mag, should someone see a criminal carrying an AR so equipped.

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  1. that setup looks clumsy. i’ve nuver used a drum magazine in an ar but as a youngster my uncle had a tommy gun with stick and fifty round drum. world of difference when you switched to the drum. from my own experience with the m16 just changing from 20 round mags to 30 rounders made a small difference in how the weapon handled. for a newbie like holmes with little or no training it made a huge difference and likely did save lives.

  2. The round count is the one remaining piece of information I’m interested in about this case. I don’t know what I’ll do with it once I have it, but I’m curious all the same.

  3. “he switched to a Smith & Wesson AR-15 equipped with a “double-drum” 100-round magazine. At some point during his heinous crime, the mag jammed. ”

    How does this square with the picture of the abandoned AR on the ground outside the door of the cinema that had a convention magazine mounted?

    • what’s the context of the picture. that could be an leo weapon set aside for a moment while they’re cuffing the suspect or helping a victim. we don’t know if that was the shooter’s weapon.

        • s.k. you’re right, they aren’t the best photos but it does look like an evidence marker next to the rifle. it would be worse than negligent if an leo laid his own weapon down amongst the evidence like that. i’m giving them the benefit of the doubt and will say that;s the “jokers” weapon with 30 round mag. so he must have done at least 1 mag change or he never used the drum unit. odd isn’t it? but news sources are famous for not getting it right, maybe he never used the drum.

        • He must of. Otherwise why would he have ordered a tactical vest that was designed to be used with STANAG magzines?

        • If I had to guess, it seems probable that he had a double feed and assumed he had run the mag dry, thus he reloaded with a 30 rounder.

        • So why did to Daily Mail call it a Colt instead of S&W? General ignorance or a second unused rifle or what?

      • All the news stories I read until the press started to twist things said that the drum was found at the scene but nobody actually said it had been used. He could have gotten a jam with the 30 round magazine.

        IMHO, the media is hyping the 100 round mag but I am willing to bet it was not used except for propoganda to have an AW Ban

        • And that’s precisely why I said (below) that magazine conjecture is best left for when the report comes out. Before that, it’s just spinning wheels.

      • In my opinion and professional experience no LEO is going to leave his weapon unattended on the ground. That’s what the sling is for.

    • I was wondering the same thing! The photo was taken durning daylight at the crime scene. Right outside the door of the theater there is an AR-15 laying there with a 30 round magazine in it, plain as day. Something is fishy about that. There is a forensics team taking photos and gathering evidence so this weapon is not a LEO weapon casually laid to the side. This weapon must be the one used but there is no 100 round drum magazine. You can find the photo if you search google images although it may take awhile. I noticed this image on a news website the day the shooting occurred before they were talking about the 100 round mag.

    • Responding to all above: I think the magazine conjecture is best left for when the report comes out. Perhaps when the 100-rounder jammed, he dropped it, swapped in a conventional 30-round, and shot it dry (or not). Remember that the first reports only said that a 100-round drum mag was found “at the scene.” Some commented at that point that it may not have even been used, but was in his car, which would still be “at the scene.” Now it’s clear it was used, and that it jammed, but we don’t know at what point that occurred or what happened afterwards.

      • I guess I’m not even sure we really know that it was used or that it jammed. With the gag order facts are few and far between (and I wish I could say the same thing about “news stories” about the tragedy). It will be a long time before enough facts become public to start to piece together what actually happened, just like Florida Our children will get to read Mas Ayoob’s analysis.

  4. 2. Double-drum magazines limit accuracy
    Do you really need to be accurate when shooting in to a crowd of people in a enclosed space? And it would be more accurate to say high capacity magazines limit accuracy, can you imagine shooting from a bench with a 100rd Surefire mag?

    3. Double-drum magazines are hard to conceal
    It would be more accurate to say, high capacity magazines are hard to conceal. Have you seen what a AR looks like with a 100rd Surefire mag?

    I’m surprised he went with the Beta magazine, it costs about 50% more than a Surefire.

    And according to Wikipedia “In November 2008 the Army Experimental Task Force (AETF) at Ft. Bliss, TX, evaluated six BETA C-MAG magazines. Four magazines—two with black covers and two with clear covers—were used with M4 carbines in three firing scenarios: controlled pair, controlled burst, and rapid fire. According to the memorandum summarizing the evaluation, the four magazines “performed flawlessly in all three scenarios without jams or stoppages.” In addition, two magazines with black covers were evaluated with M249 light machine guns in controlled burst and rapid-fire scenarios. These also performed without “issues,” according to the memo, which also notes that soldiers “had only positive comments” about the C-MAG magazines during the After Action Review (AAR).[5]”

    • Not that i’ve ever used one but Beta Co. seems to blame jam issues on a lack of graphite lubrication of magazine. If they were as problematic as people like to think, you’d think they would have gone out of business a while ago.

  5. I got one thing to say.1997 Bank of America robbery gone bat shit crazy.And look what was used and time tested.AR’s have there place and so do AK’s.

  6. well, i’ll be the one to say it: there is also the possibility that one’s state bans high-capacity magazines but allows more than 10-round magazines to be sold. strange but true.

  7. Exempted from this, of course, are the excellent 75 round RPK drum magazines. Those Russians sure know how to make a good magazine.

  8. I always thought drum mags were for the hollywood crowd (sorry). Beside the reliability issue they’re incredibly bulky, and I can only imagine the stress that 3 lb of inertia is delivering to the drum’s throat under recoil.

    There is a practical limit to mag size and weight, and this double drum crud is way over it.


  9. I shouldn’t believe a word in The Daily Mail, a newspaper that has a troubled relationship with facts.

  10. I own two 100 rd AR drum mags made in Korea by KCI. They are virtuallly identical to true Beta mags and mine feed/function perfectly. Just very heavy and not practical. Fun though!

  11. You are only fueling the gun grabbers and misinforming people by referring to AR as “assault rifle”. You people should be sued by manufacturers for doing so. AR MEANS ARMALITE RIFLE. NOTHING ELSE, NOTHING MORE. This madness must stop. Dig your own graves, not mine please.

    • First , when you went in the ARMY in 68 or 69 , on your way to NAM, You were handed an AR 15 , at this point you were told that this is YOUR ASSAULT RIFLE AN AR15. At no point in my 40 years , did anyone refer to it as an ARMALITE RIFLE, . Now it may have been sold as such, but you would never ever , ever , ever hear anyone in the service refer to AR 15 AS AN ARMALITE RIFLE.

      • Gus Raney,

        You are either senile or lying. NO ONE in the Army ever referred to an M16 as an “AR15” or even as an “AR” — only a civilian or an idiot would confuse the two other than deliberately.

        Yes, the M16 was an “Assault Rifle” because it fit the military definition of an “Assault Rifle” which was a SELECT FIRE weapon firing an INTERMEDIATE CARTRIDGE capable of being fired from the shoulder or from an assault position (basically from the hip but the Army refused to ever call it firing from the hip). The AK47 was also an “Assault Rifle” as had been the German Sturmgewehr 44. (The Russian PPSh-41 was used the same way but it was a “Submachine Gun” NOT an “Assault Rifle” because it fired a pistol cartridge).

  12. I know it’s been a few years, but really? The amount of anti-gun propaganda in this article is beyond scary. First, not such thing as an ‘Assult’ rifle. And even eluding to such is a failure in reporting. Secondly, having any practicle application for limiting magazines, adding fuel to the fire that is anti-gun liberals is 100% BS. There are zero reasons to have magazine limitations. How dare you even write, let alone publish and push through this article. TTABG has just single handedly underminded gun owners everywhere. Shame on you!

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  14. I have to call B.S. on this lame article. Non factual information all the way around. I own AR’s and I own AK’s with Hi Cap Mags and Drums. Any gun, any Mag, and any drum can jam. Drums are spring fed. If the spring is wound too tight or not tight enough it will stop feeding. If it isn’t properly oiled it can stop feeding. This is a user error. An inexperienced user error. Same as any other gun or Mag out there, not all brand and grain ammo is suitable for all guns of the same caliber. Too high of grain or too low of grain in pistols will cause feeding and jamming issues. Cheap made ammo will do the same. Some Mags and guns work best with brass casing, some with steel. To claim “drum magazines are notorious for jamming and an unwise choice” is ridiculous. Know your Rifle, know your Drum, and know what it feeds best. I can run 200 rounds through my drum with no failures firing as fast as my finger can pull the trigger.

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