I never really thougth about how fast a bullet rotates before. I understood that bullet rotion stabilized the bullet in flight and prevented tumbling but I didn't know how fast a bullet needs to rotate for that to work. I figured the math is pretty simple so I did a couple of calculations and I'm shocked at how fast a bullet really rotates. No wonder rifling stabilizes a bullet.

 

The formula I came up with is:

 

Bullet RPM = 12 / twist rate (in inches) x 60 x muzzel velocity.

 

A few examples that shocked me are:

 

A .22 with a 16" twist rate at 1,000 fps spins at 54,000rpm

 

A .223 with a 9" twist rate at 3,000 fps spins at 180,000 rpm

 

A 9mm with a 10" twist rate at 1,200 fps spins at 86,000 rpm.

Formula seems right, but your results are not:

 

.22 = 12/16 * 60 * 1000 = 45,000

 

.223 = 12/9 * 60 * 3000 = 240,000

 

9mm = 12/10 * 60 * 1200 = 86,400

 

 

Makes F1 engines seem downright slow...  

Formula seems right, but your results are not:

 

.22 = 12/16 * 60 * 1000 = 45,000

 

.223 = 12/9 * 60 * 3000 = 240,000

 

9mm = 12/10 * 60 * 1200 = 86,400

 

 

Makes F1 engines seem downright slow...

.223 makes a small turbo charger seem slow, which is a feat.

 

.223 makes a small turbo charger seem slow, which is a feat.

 

 

What is the service life of a .223 in flight?

MV x (12/twist rate in inches to make one completer revolution) x 60 = Bullet RPM

or

MV X 720/Twist Rate in inches to make one completer revolution = RPM

   

 

What is the service life of a .223 in flight?

 

A second or two. But that's because it impacts something. LEt your impeller or compressor wheel hit something and see if you get a second or two out of it.