What causes 'keyholing' of bullets?

[Goofycat]

What are the causes of "keyholing" of bullets when they hit paper,i.e., the bullet enters the paper sideways, causing a keyhole shape?

 

[jb1000br]

instability...lack of RPM's

Will happen with too little rifling twist,6mm 105 in a 10twist), or sometimes near the transonic zone,where the bullet drops below the speed of sound,308 with 168SMK).

JB

 

[garyw]

JB whats the opposite to keyholing ? what i mean is what will a bullet do if it is driven too fast i hear of over stabalizing how does this work in real terms is it physics,dynamics,??????.

 

[CPorter]

If the bullet is spinning on it's center and is mechanically sound the worse that will happen is the nose won't completely follow the bullet path and when it hit it will look like it has some vertical yaw. If the bullet didn't go in the bore straight the bullet will precess around the flight path making spyrograph looking pattern. If the bullet is spun really fast, say a light bullet is a fast twist barrel, there is a good chance the bullet will fly apart before the target. This usually happens around 50-75 yards in my experience.