Dot Physics

Somewhere on the internet, I came across this Cracked.com article on movie myths about guns. The article wasn’t too bad, but I really liked this video they included from Arnold’s movie Commando.

The myth for this particular clip was that guns never run out of ammo in the movies. Right away, I thought: I wonder how many bullets he shot? BRING IT ON.

First, I am going to find the fire rate of Arnold’s weapon. Oh, I know I could look it up on Wikipedia or something – but I am not going to do that. I am going to determine the fire rate from the clip.

After capturing an audio segment where the gun in question is fired, I opened the clip in audacity, a free audio editor. Here is what that would look like:

i-203b065669c1f416f97fec674edcc710-2010-06-16_arnie_shooting.jpg

First, I could simply count each one of those little peaks (that corresponds to a shot) and divide by the time – but what fun would that be? Instead, I will use Audacity’s ability to take the fourier transform of the sound. For a segment of the clip (the middle of the clip looks like it skips a shot or something) I get the following spectrum:

i-413b24006883511fe8489a54b576caab-2010-06-16_frequency_analysis_2.jpg

I assume the peak around 11 Hz is the gun. This would give a fire rate of 11 bullets per second. Maybe this isn’t quite right, but close enough.

If I know the fire rate (I will call this f in bullets per second) and the time the gun is fired (Δt), then the number of fired bullets would be:

i-93938280b99ebd37e40e79092fd8f529-2010-06-16_la_te_xi_t_1_8.jpg

To get Δt, I am going to look at the video in Tracker Video. Why? Because this is a great way to get more precise time measurements than if I had used Quicktime or something. Here is what I get:

  • Δt1 = 3.0 seconds
  • Δt2 = 2.8 seconds
  • Δt3 = 4.4 seconds
  • Δt4 = 4.2 seconds
  • Δt5 = 0.3 seconds
  • Δt6 = 3.7 seconds
  • Δt7 = 4.3 seconds

Those were the times I recorded while he was using his first gun. I admit that this is not quite right. Watching it again, he sometimes would pause momentarily in the middle of a “burst”. Also, I tried to be very conservative with my start and end times for the burst. Anyway, out of respect, I will take off 1 second of time. Just to make sure I am fair. This gives a shooting time of 21.7 seconds. How many bullets?

i-7e5601063befe929084d28eb77d7a3f6-2010-06-16_la_te_xi_t_1_9.jpg

That there is a whole bunch of bullets. Yes, I grant you that maybe he changed magazines at some point – but they never clearly showed that. Also, for comparison, an AK-47 has a magazine up to 30 rounds (according to Wikipedia). The M-16 also looks like it could hold a maximum of 30 rounds (I am not including the drum-feed systems because it is clear he is not using one of those).

If the Commando did indeed change magazines, he would have to do so 8 times to shoot that many bullets. That would also be pretty heavy to carry that many rounds.

Why did I just do this calculation? I don’t know.

Comments

  1. #1 Michael Seery
    June 16, 2010

    This is why I love this blog.

  2. #2 J.T. Wenting
    June 17, 2010

    I think you’ll love this site: http://www.intuitor.com/moviephysics/
    It deals with just this kind of stuff.

    Though I don’t agree with all their reviews (some seem cheesy, like their idea that Al Gore’s An Inconvenient Truth is accurate), it’s overall a pretty decent site.

    p.s. I’ve always assumed he must have reloaded in between action scenes, but maybe that’s my mind trying to put sanity in a place where there is none :)
    For a real treatise on guns never running out of ammo, see ot Shots Part Deux where Topper Harley (Sharley Sheen) eventually stands knee deep in shell casings as he fires a gun on full auto for like 5 minutes without reloading.

  3. #3 Tor Lillqvist
    June 17, 2010

    Equally weird is how the people killed / injured by Arnie’s hand grenades suddenly fly up in the air. I am certainly no military expert, but surely that is unrealistic? Isn’t the killing power of a hand grenade based on the shrapnels dispersed?

  4. #4 Lassi Hippeläinen
    June 17, 2010

    “This would give a fire rate of 11 bullets per second. Maybe this isn’t quite right, but close enough.”

    Pretty good. When I did my military service, the firing rate of an attack rifle (we used an AK47-derivative) was given as 700 bullets per minute (11.7/s). It made me wonder, because we didn’t have magazines that contained that many bullets. It would have been more appropriate to state that one magazine lasts less than three seconds. That’s why you don’t shoot continuous fire, only bursts of a few bullets at a time.

    “If the Commando did indeed change magazines, he would have to do so 8 times to shoot that many bullets. That would also be pretty heavy to carry that many rounds.”

    Not that heavy. Normally you tape three magazines together, and in a battle situation you will carry several of these packets. They are not as heavy as the gun itself. Do the math. (I’ll use this rare opportunity to say that…)

  5. #5 Jimmy
    June 17, 2010

    As #4 states you can use the magazine size of 30 bullets to calculate a magazine duration of 2.7s which in turn means that only bursts #5 (and maybe #2) would be possible.

    Also @4: I would guess that the reason for shooting in short bursts is that it is more accurate. It is not a problem that you run out of ammunition quickly if you have the same accuracy – on the contrary, that would give your opponent less time to do whatever it is you want to prevent him him from doing :)

  6. #6 Rhett Allain
    June 17, 2010

    @Lassi,

    I briefly searched for the weight of a loaded magazine, but I couldn’t find it.

  7. #7 dhogaza
    June 17, 2010

    Alas, the sound you hear is not the sound of Arnie’s gun firing during the shoot, they add the sound later. That’s why it’s constant volume as he runs around. You need to count the muzzle flashes. Maybe there’s an optical analogue to the audio tool you used for this initial analysis :)

  8. #8 CherryBomb
    June 17, 2010

    Tor, that was the thing about the video that really jumped out at me (so to speak). He must have been tossing anti-gravity bombs.

  9. #9 Neil B
    June 18, 2010

    JTW, Gores AIT may not be fully accurate but surely you don’t think that AGW skepticism is even near to being that honest and accurate?

  10. #10 Laen
    June 19, 2010

    Ammo for the M4/M16 is 5.56mm, typically you would use a 30 round magazine. You are looking at about 7 pounds for 200 rounds. The magazines themselves, depending on the manufacturer, would weigh less than two pounds for 7-8 magazines. Didn’t he steal those guns from a gun store? They wouldn’t be fully automatic anyway.

    Grenades kill with shrapnel, not the explosion…but you really don’t want to start on Hollywood’s complete lack of reality when it comes to explosions.

  11. #11 dhogaza
    June 21, 2010

    Grenades kill with shrapnel, not the explosion…

    They’re called fragmentation grenades for a reason!

  12. #12 CCPhysicist
    June 28, 2010

    @3:
    If you freeze the video at 1:11, you can see the boards that launches the dead guys almost before the “grenade” goes off. They are gray so they didn’t have to try to remove them in post production.

    There is also enough paper flying to make it pretty clear that no bullets were harmed in the making of this movie.

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