Ammo: Rounds firing as keyholes

by Erik  

Keyhole is a term used to describe rounds which are fired that do not remain concentric once they leave the barrel. Meaning, once fired the round starts wobble like a poorly thrown football or even tumble like football at a field goal. The marks which are left on paper are not round, they are oblong looking much like an old style key hole.
Keyholes can be the result of several things:
  • Wrong barrel twist/bullet weight ratio
  • Wrong amount of bullet crimp
  • Bullet defects

Keyholes will obviously decrease accuracy. It is also very dangerous to shoot rounds which are known to keyhole through a suppressor. The openings and baffles in a suppressor are very precise to allow very little gas to escape. Firing a keyhole round can possibly strike a baffle or the end cap of a suppressor thereby damaging or destroying it. Not to mention, the obvious safety concerns with shrapnel or bullet fragments coming from the end of your gun. keyhole bullets

The twist rate of the barrel and bullet weight used is important. If a barrel does not have enough twists, a heavy bullet will not spin enough to stabilize. When the bullet is not stable, it will wobble or even tumble towards it's target as seen in the picture above.

The use of match barrels or short barrels (NFA short barreled rifles) may require special ammo due to the amount of twists that it was manufactured with. Shooting any other type of ammo than what it requires will almost certainly fire unstable projectiles.

Ammo that was loaded with bullets crimped to tight or to far into the casing may also keyhole. So will bullets with defects, regardless of the correct twist ratio. A bullet with an uneven surface area will be unbalanced once it starts to spin and may also keyhole.

Last, once a bullet hits something the energy displaced can throw the balance of the bullet off. Once the bullet is no longer stable, it will start to fly like a poorly thrown football and may produce a keyhole upon impact.

The best way to ensure your gun does not shoot keyholes is to use quality factory loaded ammo or correct load data for reloads. You must also use the correct bullet weight suggested by your guns manufacturer.

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