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Comment by ars | Hacker News Reader

A gun flew into a machine and dischared with the safety still on!

http://www.simplyphysics.com/flying_objects/GuninMagnet.html

Awesome explanation of the physics of why the gun discharged here (http://www.ajronline.org/cgi/content/full/178/5/1092)

Short summary:

- A round was chambered in a safety locked gun.

- The "Sear" at the top of the gun that normally moves when the gun is fired was locked, and the empty cartridge was still in the gun, confirming that the gun was physically locked

- The pin was pulled into the unlocked firing position by the magnetic field

- The impact of the gun when it hit the CT caused the firing pin to move against the spring and hit the back of the loaded bullet, causing it to fire. There is white paint on the front of the gun where the gun hit the CT confirming the impact point

Good summary, but it doesn't quite make it clear what safety device failed. The firing pin block exists to ensure that an impact in-line with the firing pin cannot move it when the trigger is not depressed. It too could be moved by inertia, but its movement is perpendicular to the firing pin itself, so an impact cannot move both at once. In this case, the magnetic field moved the firing pin block, while inertia pushed the firing pin forward relative to the rest of the gun.

This is the only time I've ever heard of a firing pin block failure resulting in an accidental discharge.

> This is the only time I've ever heard of a firing pin block failure resulting in an accidental discharge.

The is the only time I heard of a gun encountering an extremely powerful magnetic field.

Now that's something I'd like to see on MythBusters. (Though not necessarily with an MRI machine—those things cost more than their entire budget. A large ferromagnetic coil would do nicely.)

"... At the time the weapon discharged, it was reportedly in a cocked and locked position; that is, the hammer was cocked and the thumb safety was engaged to prevent the hammer from striking the firing pin. A live round was in the chamber ..."

Round chambered, weapons discipline, not! It was reported the safety was on. I wonder if it wasn't?

No, it's pretty standard to have a round chambered with the safety on. For some models having the hammer cocked is also correct general carrying procedure, depending on the firing mechanism the particular gun uses. I do still find it worrying that a firearm would discharge in this manner. Most have multiple internal safeties to prevent accidental discharge during things like a drop from a height.

I am not familiar enough with the details of the Colt firing pin safety, but I believe 'dropped from a height' is not necessarily equivalent to 'pulled from 3ft into a 1.5T magnet'.

Please read the actual article, it answers all those questions.

They proved that the safety was on because the empty shell was still in the chamber, since the safety prevented the slide from moving and ejecting it.

"... They proved that the safety was on because the empty shell was still in the chamber ..."

Is this the first time a round has been discharged with safety on?

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