Bullet RPM Calculator???

[Dennis_in_VA]

Does have the formula for calculating bullet rpm given a specific velocity?

I found it on accurate shooter.
Sorry for the interruption.
We now return you to the show.

 

[mattj]

Re: Bullet RPM Calculator???

I don't know about the specific formula you are referring to, but if you assume that bullet takes on the full "twist" of the rifling by the time it leaves the barrel, it should be fairly easy to calculate the rpm of the bullet at the muzzle (not sure how drag would affect the rpm/fps ratio downrange)...


Given:

1:Y" rifling

X feet/second


Convert rifling twist rate to twists per foot instead of inches:

Y" = Y/12 feet --- so the rifling rate is 1 twist (revolution) in (Y/12) feet, or in other words 12/Y revolutions per foot.

So, if the bullet is going X feet in a second, and in a foot of movement it undergoes 12/Y revolutions, then the bullet will undergo X*(12/Y) rotations per second, or 60*X*(12/Y) revolutions per minute. Simplify that down, and you get the bullet leaving the muzzle at:

720*X/Y rpm

...where X is the muzzle velocity in feet per second, and Y is the number of inches per one twist of the rifling.

Assuming of course that my brain can be trusted to do math at this hour of the morning

-Matt

 

[MrMike]

Re: Bullet RPM Calculator???

MattJ hit the nail on the head, but it was confusing for me to wrap my head around, so I just put what he said in the simplest way I could.


Velocity X 720/Twist Rate = RPM

V X 720/T = RPM

Example: Your remington 700 308 has a 1:12 barrel and your shooting a velocity of 2600 feet per second, your formula should look like this

2600 X 720/12 = ?

2600 X 720= 1872000

1872000/12 = 156000 RPM

 

[The Mechanic]

Re: Bullet RPM Calculator???

http://kwk.us/twist.html

http://www.eskimo.com/~jbm/calculations/drag/drag.html

 

[CarbonMTN]

Bullet RPM Calculator — Spin & Stability