Some time ago in one of the Varmint's Hunter's Assoc. (early 90') that included a neat table showing rpm for different twist rate matched with projectile velocities........seems like the 17 Rem. was humming around 360,000rpm. I call this the 'hydraulic' effect when ground squirrels become red mist. Does anyone have this table to post up or a good formula? r in s.

back when I was in engineering graduate school I ran th ecalculations on how much energy was transferred from a spinning bullet to the target. I had the formula in a spread sheet so I could calculate the energy transfer for a variety of scenarios.

No scenario transferred a meaningful amount of energy to the target.

What WILL trasfer a lot of energy to a target is a fast-stepping, lightly jacketd .17 slamming into a ground squirrel. I have never shot one with a .17, but have no doubt it would give a really nice "mist."

You mean like this:
12 / Twist rate (in inches) * muzzle velocity (in FPS) * 60 = RPM

12 / 10 * 2900 * 60 = 208,800 rpm (typical 150gr 30-06 loading)

close but not quite. The formula for rpm would be:

(1 rev/TWIST in) (12 in/1 ft) (VELOCITY ft/sec) (60 sec/ 1 min) = X rev/min

You need to have everything except "revolution" on top and "minute" on bottom cancel out. So in your example it would be 10/12, not 12/10.

But the rpm does not give you an indication of "misting ability." I don't remeebr all of the related formulae, but do remeber the results of the number crunching.

Hydralic effect is another matter entirely, and is still debated over if it truly exists and how it actually works if it is present.

Hit a squirrel with a thin jacketed bullet moving quickly and it will be nothing but a messy memory.

Try 720xVelocity(fps) divided by twist(in inches)
So your 17 Rem is approx 288,000 rpms for a bullet traveling 4000 fps out of the std 10" twist- I've heard of the buzzsaw effect, but can't say I've experienced it.

Marc
I'm just a working Tech, not a engineering graduate, but the last I looked a 1-10 twist turns the bullet MORE than 1 time / foot, correct?
12/10 (my way) gives 1.2 turns in a foot while 10/12 (your way) says it only turns .833 times in a foot.
Which is it?

When setting up an equation, you have to look at what the units are and cancel out the units to get the answer in the desired units. Man I wrote that and just confused myself!

Anyway, you must first define your desired units for your answer (in this case revolutions/minute). units are canceled out by dividing them by themselves. for example, if you want to know what fraction in hours a certain number of minutes is, then you would write it:

(45 minutes)(1 hour/60 minutes)=.75 hours

In this case, 1 hour equals 60 minutes, so dividing dividing 1hr/60min gives you a value of "1", which of course will not change the value of the answer. What that does is give you the same number that was already there, but in the units you desire.

I can't type, so this is doubly hard for me to explain here. If I could write this on a white or black board, it would take all of 2 minutes. But I am limping along the best I can!

Anyway, to use your example of an '06 shooting a 150gr bullet at 2900 fps:

(1 revolution/10 inches)(12 inches/1 foot)(2900 foot/1 second)(60 second/1 minute)=208,800 revolutions/1 minute

Which is also JUST what YOU had!!! I worte it on a piece of paper last night and then when I looked at the screen I turned dislexic or soemthing. Thanks for pointing out my error!

Hydraulic Effect refers to the situation wherein the bullet hits a vein, artery, heart and, because water or blood is incompressible, transmits the shock throughout the body. I recall first hearing the term way back in history when some guru de jour was extolling the effect of the 220 Swift on deer. I'd call the results of high RPM the Dremel Effect .

Bud W

The "red mist" was thought to be a result of "hyrdostatic shock", but in reality it is the result of a projectile merely tearing through blood vessels and arteries and spewing the contents into the air.

I remember back in 1969 when the Marine Corps first issued me the M-16, it was said by folks who didn't know better, the Army, Navy and Air Force, that the small caliber bullet travelling at such a high rate of speed would cause hearts to literally explode if the bullet hit near a major artery. Of course these same folks concocted the myth that the bullets fired from the M-16 tumbled.

I am aware of the term "hydrostatic shock," which I have also heard many people call "hydraulic shock" or soemthing else along those lines. THere is still debate whether this is a real occurence or just what happens with an expanding bullet in the innards. SOme people think it akin to a lightning strike, and some think it a low grade of hog wash.

Personally, I stay out of those arguments! It is like when people debate the merits, or lack there of, of the temporary stretch cavity that can be measured in ballistic jelatin. For some reason both sides often get pretty heated in their defense of their position.

Irregardless of whether it actually makes a difference or not, one thing is for certain-the amount of energy transferred to a living being via the rotation of the animal is trivial and falls out of the equations.

Ahhh yes Malm. Happened when I was a wee pup, but I grew up hearing about the "buzz-saws" coming out of the M16 barrels.