RPM calculator

[Bloodman14]

Wasn't sure where to put this; who has the formula to figure the RPM's of a boolit? Need it for a PowerPoint for my speech class. Thanks!

[AzCaesar]

Assuming muzzle velocity in Feet/Sec and twist rate in inches, it should be

720*(muzzle velocity)/twist rate

[lwknight]

Divide 12 by the twist
Then multiply the answer by 60.
Then multiply the next answer by feet per second.

Say you have a 10 in 12 twist 30-06 : 12 / 10 = 1.2
So 1.2 X 60 =72
Then 72 X 3000 fps =216,000 rpm's

[lwknight]

Welcome aboard Az Ceaser.

The 720 X Velocity / twist is a lot simpler.

1 FPS = 720 inches per minute.
3000 FPS = 2160000 inches per minute
Divided by how many inches it takes to make a 360 degree turn.
2160000 / 10 = 216000 rpm's

I like that a lot better.

[Bloodman14]

:holysheep That is fast! I hope the class can grasp that kind of technical info.

[Wayne Smith]

Ha! You can do an entire speech just on how to figure the RPM's. Then another on what that means.

I should warn you though - I'm a Psychologist and the State of New Hampshire was trying to decide what score to set for passage of the National test for Psychologists. The Board and committee wanted one standard deviation above the mean. Now, understand that the State of New Hampshire has the largest lower house of Congress of any state - 420 members, not all of them well educated. The Statistics Professors at the University of New Hampshire advised the Board to go for the Mean, not one SD above. The reason? They did not believe that they could explain the concept of a standard deviation adequately for the State Legislature to understand!

When you try to explain abstact or obtuse mathematical concepts expect a lot of blank stares.

[old turtle]

What is scary is that most people in the U. S. Congress know very little (nothing) about math or science. Yet are making decisions every day that affect our lives based on what they think they know.

[Bloodman14]

Wayne, you mean I may have to 'dumb down' my explanation?:roll: Great, that will solve the problem!:(

[Rocky Raab]

This is for Missourians? Easy.

"Boys, the faster they goes, the faster they spins. Yessir, that there rifle bullet is a'spinnin' faster'n a turpentined cat."

[AZ-Stew]

:holysheep That is fast! I hope the class can grasp that kind of technical info.

Compare it to something they do understand:

An electric fan, on high speed, runs about 1,700 RPM.

Your car engine, at 65 MPH, turns about 2,000 RPM.

When you accelerate your car really hard, foot to the floor, trying to get on the freeway, the engine may approach 5,000 RPM before the transmission shifts.

A NASCAR race car engine turns 8,000 - 9,000 RPM.

A jet engine on a Boeing 767 airliner turns 11,000 rpm.

A Formula 1 race car engine turns over 15,000 RPM.

Then there's the bullet...

Regards,

Stew

[EOD3]

What is scary is that most people in the U. S. Congress know very little (nothing) about math or science. Yet are making decisions every day that affect our lives based on what they think they know.

IMHO: most politicians are just one rung above shoe salesman and should never be trusted with anything more complicated than a crayon.

I don't remember who said "It isn't what he doesn't know that bothers me, it's what he thinks he knows and is dead wrong about."

[chboats]

EOD3 - That was a real insult to shoe salesman.

Carl

[Rocky Raab]

Stew, the fan section of a jet engine (basically a glorified propeller) turns at 10-12,000 rpm, but the core (the actual jet engine) turns at about 65,000.

Still, bullets do wind up, do they not?

[AZ-Stew]

Rocky,

I wasn't a jet mechanic, so I relied on what looked like a reliable post here: http://www.airliners.net/aviation-forums/tech_ops/read.main/156501/

It's reply #12 (on the left, just below the bold-type poster's name) , about half way down the page, posted by DI757md.

I'm sure there are military jet engines that turn faster, as I remember reading such many years ago, but that's what I found, and it makes the point within the list.

Anyway, thanks for the input.

Regards,

Stew

[NSP64]

Different size jet engines and different parts of that engine spin at different rates, but the tips of the fan blades should never go super sonic.
I think a more accurate description of bullets/boolits should be in RPS (revolutions per second).
3000 fps/.833333(10" twist((10/12))=3600.0144 RPS


I like RPS because it is smaller numbers and easier to latch onto. Plus no bullet has a flight time of 60 seconds

a 180 gr bullet launched at 3000 fps out of a 1-10 barrel with bc of .420 has a time of flight of 0.104 seconds to 100 yrds, so it spins 374.401 times by the time it gets there.
Same rifle (1-10) shooting a 180 boolit with bc of .250 @ 1800 fps has TOF to 100 yrds of 0.181 seconds , will spin 390.962 times when it gets there.

[AZ-Stew]

I like RPS because it is smaller numbers and easier to latch onto. Plus no bullet has a flight time of 60 seconds

Some artillery will run over a minute. A 16 inch Naval rifle (battleship 16 inch gun) will do it, but the rifling twist rate is slower. The definitive web site (http://www.navweaps.com/Weapons/WNUS_16-50_mk7.htm) says the twist is 1:25. Unfortunately, it doesn't tell us whether it's 1 turn in 25 inches (not likely), 1 turn in 25 feet, or 1 turn in 25 calibers (25x16").

The problem with RPS is that there's nothing in most folks experience to compare it with.

Regards,

Stew

[NSP64]

Some artillery will run over a minute. A 16 inch Naval rifle (battleship 16 inch gun) will do it, but the rifling twist rate is slower. The definitive web site (http://www.navweaps.com/Weapons/WNUS_16-50_mk7.htm) says the twist is 1:25. Unfortunately, it doesn't tell us whether it's 1 turn in 25 inches (not likely), 1 turn in 25 feet, or 1 turn in 25 calibers (25x16").

The problem with RPS is that there's nothing in most folks experience to compare it with.

Regards,

Stew

I would need a lead sled for sure.LOL
I can relate to something turning say 350 times in 100 yrds as opposed to 320,000
If I remember right our 8" guns didn't turn once in the length of the barrel.

[RP]

You know the members on this site are so full of information it never stops surprising me. Makes this a great place to hang out. Thanks guys for all your input if i have a ? I can alway come here and get a answer fast.

[Echo]

IMHO: most politicians are just one rung above shoe salesman and should never be trusted with anything more complicated than a crayon.

I LIKE that!

I don't remember who said "It isn't what he doesn't know that bothers me, it's what he thinks he knows and is dead wrong about."

Josh Billings (a nom de plume) was a cracker-barrel philosopher was one who came close - "It ain't what he doesn't know that bothers - it's what he knows that ain't true!". I'm sure there were others. It is universal...

[Echo]

I would need a lead sled for sure.LOL
I can relate to something turning say 350 times in 100 yrds as opposed to 320,000
If I remember right our 8" guns didn't turn once in the length of the barrel.

One of my most favorite profs in grad school was a Naval Acad graduate who was gunnery officer on the USS Nashville. He told us in class that he had best success against kamikazes with his main battery. I looked it up, and he had >15< 6" rifles in his main battery (5x3)! He had each turret maintain 3 special rounds for each gun, one fused for 3,000 yard, one fused for 5,000 yards, and one fused for 10,000 yards. When the entire main battery fired at a single high-speed bandit coming in, he said his thought was "Fly through that ellipsoid, you bastard!".

God, I miss him...

[EOD3]

EOD3 - That was a real insult to shoe salesman.

Carl

Well, you know how it is, everyone looks down on shoe salesmen... :razz:

[Doc Highwall]

Not my hero Al Bundy.

[Bloodman14]

It's amazing how a simple question leads to a plethora of related answers that put things into a kind of practical perspective. Thanks, guys!:Fire:

[Bloodman14]

Follow-up question; does anyone have a graph of some kind that shows how many people reload and what? Google turned up garbage I can't use.

[lwknight]

Gunnard , I think you just found the impossible question. Its right there with " how high is up? "

[Rocky Raab]

RCBS posts a list of the previous year's most popular die sales. That gives an indication of what people load, but not how many people do it. Most folks reload for more than one cartridge - even if they start out to only load one!

[azcruiser]

You could try the National Reloading Manufactures Association . They used to have a flyer on stuff like that .

[theperfessor]

Even knowing new die sales doesn't really tell you anything about the volume of cartridges in individual calibers that are reloaded. Just looking in my own die collection, I find three dies sets that haven't been used yet - 45/70, .270, and 7.5 x 55 Swiss, and die sets that have been used to reload thousands of rounds. primarily 38/.357, .44 Spcl/mag, and .45 ACP. I'll never wear them out and I'll never replace them with new ones. They were all new at one time and showed up on Lee's or RCBS's sales figures for that year.

And casters like us throw another monkey wrench into the works. It means you can't correlate bullet sales (primarily J-bullets or swaged lead pistol slugs) with specific cartridges.

I know this isn't what the OP asked, no intent of thread drift here.

I would bet that the most volume of cartridges in specific calibers reloaded probably has .38 Spl and .45 ACP at the top of the list, with 9mm, .40 and the two .44s combined right up there. Then you'd probably start seeing rifle cartridges (.223, .308, 7.62 x 39) on the list. After that?