Looking Through The Keyhole

Yet more reader questions are answered.  This time around, it concerns yet again my past post on derringers.

I heard that derringers will usually keyhole.  Is that bad?”

Is keyholing bad?  Yeah, pretty much.  But to understand why we must first discuss what is meant by keyholing.

The way to make bullets stable in flight is to give them a spin.  If they are revolving around their long axis while flying downrange, they will be much more accurate.

bullet spin

This spin is imparted to the bullet by the rifling cut inside of the barrel.  But what happens if the barrel is so short that the bullet pops out before it has time to start to spin around the long axis?  If that happens, the bullet most usually starts to tumble around any old way.

tumbling bullet trajectory

This significantly reduces the range and accuracy of the shot.  The bullet tends to drift around wherever it likes, wandering about like a dog sniffing trees.  Not only that, but it also tends to strike the target in some way other than nose first.

KeyHole-Tear-1

KeyHole-Tear-2

(Picture source.)

Those might not look much like keyhole, but the name comes from the wounds that are made by such tumbling bullets.

keyhol bullet wound in skull

old keyhole

Not a perfect match, it is true, but descriptive nonetheless.

So tumbling bullets can produce oddly shaped wounds, and those wounds resembled a keyhole shape.  Why are all tumbling bullets referred to as keyholing, since all of them do not produce such shapes when they strike the target?  Pretty much because people think it sounds cool.  (“My gun is keyholing!“)

Getting back to derringers, their short barrels increase the chance that the bullet will not pick up enough spin before it leaves the barrel.  This doesn’t mean that every shot from a derringer will keyhole, but it does seem to be a fairly prevalent situation.

engraved derringer

Okay, so bullets that tumble are not as accurate, nor do they have as great a range, as bullets that behave themselves and spin in the proper manner.  This problem is relatively common with derringers.

But is it really a problem?  Derringers are not known for their long range accuracy, and are intended to be used against violent criminals that are right on top of the defender.

angry man pointing finger

Who cares if the bullets tumble?  They will still hit as hard, won’t they?

Tumbling bullets do tend to slow down much faster than those which spin due to air resistance, and derringers are intended to be used against targets that are close enough that this wouldn’t be much of a factor.  But keep in kind that tumbling bullets also tend to strike the target at an odd angle.  This means any defensive ammunition used, such as hollow points, won’t work as advertised.  They have to hit nose first in order to expand.

expanded hollowpoint bullets

Obviously, this isn’t going to happen if the bullet strikes the criminal any old way.

If one favors boring old ball ammunition, then one should be pretty confident that their derringer will work about as well whether or not the bullets tumble.  But if one pays for defensive ammo, then bullets which tumble can mean that the extra cash was wasted.

3 Responses to “Looking Through The Keyhole”

  1. Fruitbat44 says:

    Please correct me if I’m wrong, but I always thought that a bullet that tumbled would do more damage to an attacker than one which didn’t.

    This of course leaving aside hollow-points and such which, as pointed out, rely on arriving nose first to expand.

  2. The purpose of a derringer is to cause a wound that bleeds internally. The preferred target for a normal pistol is the heart and lungs; the preferred target for a derringer is the intestines.

    The goal is to make the target die of internal bleeding or infection, and that will happen even if the bullet does tumble. As Fruitbat44 says, a tumbling round will cause a lot of bleeding — assuming it hits.

    The big problem with a tumbling round is that it veers off unpredictably. But a derringer is also not a long-range weapon. Within 6 feet of the target, that factor won’t matter.

    And yeah, the preferred ammunition is FMJ, not hollowpoint.

  3. […] Some time ago, I posted an essay concerning how bullets fired from derringers can tumble in flight. […]

Leave a Reply