KIND OF A TECH QUESTION.. DOES ANYBODY KNOW HOW MANY RPM OR RPS A BULLET IS TURNING WHEN IT LEAVES THE MUZZLE?? THERE MUST BE A TABLE OR CHART OR S0METHING SOMEWHERE....................... A .357 MAG CAN BE YOUR BEST FRIEND..........

It would depend on the velocity of the bullet and the twist rate of the barrel.

Seems to me it'd be 12/barrel twist * velocity in fps for revs per second (rps).

tasco 74.....it would be easier to read your posts if they weren't all in "caps".

TASCO 74....IT WOULD BE EASIER TO READ YOUR POSTS IF THEY WERE ALL IN "CAPS".

This was a test...which was easier to read?

TASCO 74

SAY THE BULLET DOES 3000 F/S AND HAS A 1 IN 12 TWIST.

THEN IT TAKES 1/3000TH OF A SECOND TO GO 1 FOOT AND IN THAT TIME THE BULLET TURNS ONCE. THEREFORE IT WOULD TURN 3000 TIMES IN 1 SECOND OR 180000 RPM

WITH A 1 IN 10 TWIST IT WOULD SPIN FASTER.

MIKE

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Tasco 74,

Say the bullet does 3000 f/s and has a 1 in 12 twist.

Then it takes 1/3000th of a second to go 1 foot and in that time the bullet turns once. Therefore it would turn 3000 times in 1 second or 180000 RPM.

With a 1 in 10 twist it would spin faster.

Mike

[ 09-02-2002, 10:35: Message edited by: Mike375 ]

Tasco, try this:

(assuming twist measured in inches, velocity in fps)

720 x (velocity) / (Twist)

ex:
If you have a 1:20 twist on your pistol, and you shoot a bullet at 1500fps,

720 x 1500 / 20 = 54000rpm

[ 09-02-2002, 10:56: Message edited by: ScottB ]

The first approximation calculation of projectile RPM should be calculated as above.

We did some testing with a Clerke pressure gun in .223. The fixture had two pressure sensors ... one at the end of the chamber and the other at the forward location of gas port in an M16 20" barrel.

Residence time of the bullet in the bore was measurable ... we were taking data at 50,000 points per second. Residence time turned out to be 3.5 milliseconds ( = 0.0035 sec) at SAAMI max pressure as I remember it.

I don't think this calculates to the same RPM value as given above ... but is higher.

Without actually testing a specific projectile in a bore of the same twist and of similar construction (button, cut, micro groove, etc rifling) probably best to suggest that bullet spins "damn fast" and leave it at that.

In figuring RPM, the above formulas are correct. Most rifle cartriges come close to 200,000 RPM. This is why bullets that expand with sharp petals (like the Barnes X or Bearclaw) have greater shocking effect than bullets that expand into a smooth lead mushroom. The petals not only do more damage, they also throw fragments of bone, etc. outward creating even a larger wound channel.
The RPM sounds like a huge number, but it is spread out over a long lineal distance. It is not like a stationary drill bit spinning that fast, the bullet is only spinning 1 revolution per foot that it travels in distance. It is the forward speed that makes the RPM's so high.

wow thanx guys ..

a .357 mag can be you best friend.......