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RPM of bullet

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gbh

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Sep 12, 2002, 10:51:05 AM9/12/02
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How many RPM does a typical rifle round spin?


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Chris Johnson

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Sep 12, 2002, 9:45:35 PM9/12/02
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It's often in the range of 200,000 to 300,000 RPM.


Consider a .223 at 3000 FPS coming out of a 1 in 7 twist
barrel. The bullet makes 1.714~ revolutions per foot, and
multiply that by 3000 FPS. That's 5142.85~ rotations per SECOND.
Multiply by 60 to get RPM, and you get 308,571.4~ RPM.

Calculating for a 1 in 12 twist barrel is dead simple. In
that case, it's muzzle velocity in FPS times 60 to get RPM.

CJ


gbh wrote:
> ...

Clark Magnuson

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Sep 12, 2002, 9:47:53 PM9/12/02
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[velocity in feet per second] [60 seconds per minute][12 inches per
foot]/[twist rate in inches per revolution] = spin rate in revolutions
per minute [rpm]

Example: 30-06 shoots a bullet 3000 fps out of its 10" twist barrel
Solution: [3000 fps][60 s/m][12 in/ft]/ [10"/rev] = 216,000 rpm

Arthur Erhardt

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Sep 12, 2002, 9:48:03 PM9/12/02
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gbh <scanner...@yahoo.com> wrote:
# How many RPM does a typical rifle round spin?
If nothing's broken (i.e. bullet doesn't hop over the lands inside
the barrel), you can calculate that from twist length and
initial velocity.
Example: (Pistol ; I'm not that familiar with rifle specs).
Glock 19, twist length 250mm (i.e. 4 rotations on 1 meter of
way), v_0 = 410 meters / second with light 95grs bullets:

410 m/s x 4 r/m = 1640 rotations/second
x 60 seconds / minute = 98400 rpm.

Rifle bullets are usually much faster (800 .. 1000 m/s), and IIRC the
M16 barrel has something like 160 mm twist length.

Regards,

Arthur

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Jerry Thomas

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Sep 12, 2002, 9:49:57 PM9/12/02
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Twist rate of the barrel (Turns per foot) times the muzzle velocity
(fps) of the projectile times 60 seconds per minute. 10/12*2800*60 =
140,000 RPM

gbh wrote:
# How many RPM does a typical rifle round spin?

--
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It is the argument of tyrants; it is the creed of slaves.
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John Kepler

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Sep 12, 2002, 9:56:15 PM9/12/02
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# How many RPM does a typical rifle round spin?

It depends on the TR of the barrel and the velocity of the bullet, but for a
rifle round the average range is between 175,000 and 250,000 RPM (and no, I
didn't hold the "0" key down too long, the numbers are correct).

John

nataS

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Sep 13, 2002, 6:34:03 AM9/13/02
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"gbh" <scanner...@yahoo.com> wrote in message news:<alq9kp$ndm$1...@grapevine.wam.umd.edu>...
# How many RPM does a typical rifle round spin?

Pretty easy to figure in a ballpark range, but for exacts you'll need
specifics, namely:

Twist rate of the barrel.
Velocity of the bullet.

T = Twist rate of the barrel, in inches per revolution
V = Muzzle velocity of the bullet, in FPS

RPM = (12/T) * V * 60
^^^^^^ ^^^^^
(converts inches to feet) (converts seconds to minutes)

For the sake of argument, lets say you're shooting an AR-15 with a
muzzle velocity of 2800 fps, and a twist rate of 1/7

RPM = (12/7) * 2800 * 60
RPM = 288,000 RPM.

For a .44 Mag with a muzzle velocity of 1400 fps and a twist of 1/20,
50,400 rpm.

Trenton G. Twining

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Sep 14, 2002, 9:23:11 AM9/14/02
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gbh wrote:
#
# How many RPM does a typical rifle round spin?
#
In the neighborhood of 250K RPM wouldn't be unusual. But it varies.
You should do the math for the particular rifle: how far the bullet
travel per minute divided by have far it travels per revolution.

2750 ft/sec * 60sec/min = 165000 ft/min

165000 ft/min * 12in/ft = 1980000 in/min

1980000 in/min * 1/9 rev/in. = 220000 r/m (AKA RPM)

This could be reduced to muzzle velocity in (ft/sec) * 720 / in. per
turn of the rifling. The RPM changes very little in the course of a
bullets flight.
--
Trenton G. Twining

Personal:
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PShovestul

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Sep 16, 2002, 10:49:31 PM9/16/02
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It depends. If you know the muzzle velocity (say 2500 ft/sec) and the rate
of twist of the barrel (say 10 inches per revolution) you can calculate it.

(2500 feet/sec X 60 sec/min X 12 in/ft) / 10 inches/rev = 180,000 rev/min

Paul Shovestul

"gbh" <scanner...@yahoo.com> wrote in message
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