Twist, RPM, Velocity and Temperature

M

Muddyboots

Moderator
Staff member
What do we know? What is the relationship of how twist, RPM and velocity generate additional bullet temperature and effect on terminal performance? Effect on the "triangle"? Velocity, temperature, RPM effect on petal disbursement and in what condition? Curved? Flat? How does increased temperature affect performance? 🤷🏻‍♂️ What is optimum RPM (and temp?🤷🏻‍♂️) to generate terminal performance efficiency? Is there a RPM range that yields the WOW? Does temperature accomplish anything?

What's out there? Here is one study that acknowledges the temperature of bullet in flight in public literature is sparse.

www.ncbi.nlm.nih.gov

Temperature Measurement of a Bullet in Flight

This study answers a primary question concerning how the temperature changes during the flight of a bullet. To answer the question, the authors performed unique research to measure the initial temperatures of bullet surfaces and applied it to four kinds ...
www.ncbi.nlm.nih.gov www.ncbi.nlm.nih.gov

I recommend 3 fingers of Jim Beam!
 
Gday
Muddy & I had a great conversation & been ticking on it a little bit more

I’d hope @T_the_Tinkerer can weigh in on his recent gel tests or ones we chatted about of the petals on a pill cut the gel not crushed

I don’t want to put you on the spot @cbjr
But then you know me lol
So how do you see this playing out on the hammers alloy among the differences on the terminal side eg does a hotter pill create a easier path or more resistance in tissue 🤷‍♂️etc etc etc

Think of how quickly copper accepts heat a dissipates it fairly evenly & a great example is you grind or drill a hammer you can’t hold it for to long before the heat gets to hot & worked out gloves needed lol where a c&c I used to do those no worries

So what do we get by shooting a higher rpm pill
History for me
I thought that a high rpm would fling those petals really quickly & go sideways really quickly
Oh I was wrong again as we can tune a pill from the depth ,width of the hp plus the nose profile also shows it’s traits & get extremely impressive penetration from such little/light petals that cut not crush
Usually that’s not a copper thing it’s a brass thing

That’s enough for now as I’m getting ahead of myself lol & need to breathe right @kneedeep

Pluses & minuses so let’s get into them
No right nor wrong just a ticking & hopefully a better understanding

Cheers
 
I read it.

I still have no idea if bullet temperature is even important, really?

I do know that bullet nose shape and hollow point depth is critical. You can modify either (or both) and differences in bullet performance/behavior are readily observable and measureable.

Think I'll wait for cliff notes to decide if this temp thing is even worth the energy😝
 
@Farleg
By the looks of it, bullet temperature seems to decrease rapidly in the first seconds. Without knowing the second point of testing, I can't say by how much. I feel like bullet temp, according to the posted study, isn't affecting any thing for us. Their highest temp was 94⁰C/~200°F. Hard to say what a 101 from the rum would be. Let alone a 125hht from a cm.
 
Some of this temperature thought comes observations of perceived "carbon" at gel entry point. The higher RPM's from higher velocities faster twists. When you see something as part of an experiment (shooting gel is technically an experiment), there should be thought for effect. As @gltaylor mentioned, maybe nothing but the curiosity factor makes me want to chase it down.

Is the carbon result from the bullet temp? High velocity? Hmm are we cleaning our barrels? 😂 🤷🏻‍♂️

Copper is terrific heat sink so is this a heat transfer? How does heat transfer affect entry? 🤷🏻‍♂️

The bigger question is since using faster twists, higher velocity, yielding much higher RPM's, is there an option bullet RPM, for optimal bullet terminal performance? Is there a target bullet RPM to consider even for barrel selection? Is this RPM, dedicated to type of bullet? HH versus HHT?

Haven't had coffee yet so give me break!😂
 
You can scroll down to their conclusion.
Excluding the 9mm
The 7.62x39 had a .1° difference beginning to and and 14.6° at the muzzle.

7.62x51 had a -4.2° reduction at the POI which is interesting but I give that to the “material” used. With only an 8° rise at the muzzle.

To Farlegs question about heat I’d say it’s neutral. Since most of these test shots were at a close range. I’d suspect beyond hunting range any temperature increase from the bore is dissipated at 75-xx hundreds of yards.

Frictional heat from the bullet flying through the air will add 3.5°-4° at most with copper (150gr bullet as a standard). But as we saw with the 7.62x51 the efficiency of the nose will actually cool at distance.

Which leaves us with the petals.
Higher RPM’s “should” make petals disperse with more concentricity than a lower RPM.

At what point do the petals break off is a good PH.D paper

My theory is
A). They shed instantly due to hydraulic pressure snapping them off at the base of the petal and the peel back effect we’ve seen are the petals making their way through the hide, material, and organs.

B). They shed off within a few thousands of a second with the hydraulic pressure peeling the nose back on the petals and shedding them off almost at the same time.

I suspect it’s A). Only because Steve and Brian’s goal is to allow the core of the bullet to do the work and if a single petal remained on the core it will cause the bullet to divert off center course.
 
so do you feel there is an optimal RPM for petal disbursement for highest efficiency of terminal performance?
 
Muddyboots said:
so do you feel there is an optimal RPM for petal disbursement for highest efficiency of terminal performance?
Click to expand...
Terminal performance.
I believe if you get high density gel and a high dollar slowmo camera zoomed in you should be able to see the point it breaks off then reverse engineer the math to see what PSI it’s shedding.
During the same test you should run it with a super fast TR and a standard TR.
 
OutdoorEdventure said:
I believe if you get high density gel and a high dollar slowmo camera zoomed in you should be able to see the point it breaks off then reverse engineer the math to see what PSI it’s shedding.
During the same test you should run it with a super fast TR and a standard TR.
Click to expand...
I agree with this. Myself and couple others have been discussing this for a while as it would answer multiple questions.

The frame rate of the camera would have to be extremely high to actually see the nose coming apart. The gel would also have to be extremely clear and be able to transfer the amount of light needed for these high speed cameras.

The shank velocity could also be calculated after the petals are shed. Knowing the shank velocity, the shank energy could be calculated. From this you can figure the amount of kinetic energy needed to shed the nose petals of a given nose/petal design. All useful information when designing a pill.

This would also answer my speculation about how different nose/petal designs come apart. Example, the nose designs that peel vs the ones that pop and then then the HHT design that I believe does both when properly balanced.

Petal dispersion would definitely be interesting to see.

Kneedeep
 
@Muddyboots

Your opening line of questioning couldn’t have been much broader! A lot of fine details to work out, so keep throwing more research and results out.

I appreciate you linking the research. The results of heat on the nose of the bullet are not close to the numbers I read in the past. Example, a number that I’ve read in the past was a bullet can generate up to 400-600 degrees Fahrenheit on the nose. There was no research to back these numbers up. Hornady’s heat shield tip was spurring on these discussions. From muddy’s research he linked, hornady’s observed tip melting on the Doppler radar might be a big hoax.

I picked up some useful information from this research but it also has me wondering about a few things. First the middle of the bullets produced the most heat, likely from the friction of the bearing surface of the bullet on the rifling. The fact that the tip of the bullets and the base of the bullets don’t show a lot of difference in heat makes me speculate that heat from the friction (dispersed from the middle to the ends) overrides the heat from the hot gases on the base and any friction with air on the nose.

It’s also eye opening that all heat decreased with time and distance.

I also noticed that the slowest moving bullet (38 special) created the most heat in the middle. I didn’t see any specs on barrel lengths so I’ll assume the two pistol cartridges were short barrels and the rifles were longer barrels. I would have guessed that a longer barreled rifle with more velocity would have created the most heat. This is proven to be wrong. So from this, would a 4k bullet produce more or less heat? If the trend follows this research, there would be less heat, if the bearing surfaces and bullet/barrel fit were similar.

I don’t see any issues with tips melting after reading this. Unless there’s better research to prove otherwise.

Thanks muddy
Kneedeep
 
@Muddyboots

As far as heat regarding terminal performance, I don’t see any real affects. But you can prove otherwise. At what point is a bullet or fragment too hot that it cauterizes the wound? This process generally takes a glowing red piece of metal, so I don’t see this as a factor.

I believe it’s all in the pressure and amount of tissue that is affected when a bullet goes through an animal.

As far as extreme twist rates, you can visually see a difference in gel when using copper pills that hold their petals. The 8.6, 3 twist vs a 7? Twist. I don’t remember exactly. You can look it up on YouTube. The faster twist produces a larger bubble. But, does this translate to shedding petals?

@Farleg didn’t see a big difference with his 7 twist vs (I believe) 11 twist. The 7 twist did straighten out some shanks that otherwise turned in his slower twist. A bandaid for an unbalanced pill in my opinion.

Throw your results into the conversation muddy. Maybe something will come out of it. We’ve all been wrong when speculating what happens. Well I certainly have as Farleg is certain to feed me crow soon enough.

Kneedeep
 
cbjr said:
@Farleg
By the looks of it, bullet temperature seems to decrease rapidly in the first seconds. Without knowing the second point of testing, I can't say by how much. I feel like bullet temp, according to the posted study, isn't affecting any thing for us. Their highest temp was 94⁰C/~200°F. Hard to say what a 101 from the rum would be. Let alone a 125hht from a cm.
Click to expand...
Gday cbjr
👍
Ok the next part of the equation
From a structural point of the plains & slip in the hammers alloy as copper is a good conductor of heat transfer do we get a reliable pill that @ various temps ( eg in the minus to well over 70degree Celsius)
That the alloy itself @ moment of impact is actual a fairly constant temperature

@kneedeep no crow yet 🤪that makes sense on quaterisation but also the old smoking wallaby comes to my mind so the thoughts a keep a ticking on that one 😇

On twists mine was originally a 12 & the 7 increased the rpm by roughly 2/3 rds & totally agree as if you get a very well balanced pill you don’t need the twist ( anybrand )
What I’m also watching closely is the general pill lengths then the delving deeper side of it , calibre to overall pill length ratio & calibre to Shank ratio as this is where extra twist is needed once you step outside the sweet spot

It dosent seem to be a weight thing as much as it is a length thing

What I like to have is around the 1 extra twist from advertised as a good rule of thumb to give us a little insurance where I probably should be paying more attention to the rpm but I want a balanced pill regardless

Cheers
 
Muddyboots said:
Absolutely GREAT stuff! The one thought I have is to have switch barrel with 2 different twists to test same load in same rifle in different barrel twists.
Click to expand...
Can’t wait to see your results head to head.

I personally don’t think about RPMs regarding bullet twist. I feel RPMs are a hype number because it’s in the hundreds of thousands of rotations. I don’t shoot far enough for a Minute to elapse. I shoot in seconds and a couple of seconds is a lot. Just ask my wife.

When I think about twist and shedding the nose, I think about the thickness of the hide, meat and rib bones. The average shot for me. On our deer this equates to roughly 1.5 inches.

So my 308, 12 twist equates to 30 degrees of rotation per inch of travel. In 1.5 inches to penetrate through the ribs, that’s 45 degrees or 1/8 of a turn of the bullet.

Now my 300PRC 8 twist equates to 45 degrees of rotation per inch of travel. In 1.5 inches to penetrate through the ribs that’s 67.5 degrees or 1/5th of a turn of the bullet.

If I had a 3 twist (similar to the 8.6 I’m watching closely) that would equate to 120 degrees per inch of travel. In 1.5 inches to penetrate the ribs, that’s 180 degrees or 1/2 of a turn of the bullet.

So my two practical twist barrels don’t even rotate a quarter of a turn while a majority of the petal shedding is happening. In my mind extra twist is a bandaid for unbalanced pills and pills that are getting too long for caliber. The extra twist helps stabilize the shank and likely increases straight line penetration. Farleg has seen this.

Now for the extreme twist, ie 3 twist, I’m undecided about the actual result regarding shedding monos. I feel the increased twist of the resulting shank would not only ensure straight line penetration but the extra rotation of the shank could cause more cavitation. Resulting in more permanent damage to the organs.

Just my 2cents
Kneedeep
 
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