Fastest possible bullet in theory?

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Dizzipator

New member
Flywheel Stress

There’s one other consideration that I didn’t see mentioned, in so far as limitations on the rotation speed of the projectile.

Spin the bullet too fast and it will be torn apart when the hoop stress exceeds the tensile strength of the bullet.

An old time MIT trained mechanical engineer (Class of 57 or so) I used to work with loved this bit of trivia -

What’s the fasting rotating tool in common usage?

Rifle bullet. On the order of 240,000 RPM in high speed/small caliber bullets.

And then he would point out that bullets are limited in rotational speed by the hoop stress factoid above, which limits rotating projectile top speed simply by the needed rotation-speed-for-stability exceeding material strength if you go too fast.

It isn’t just that smooth bores aren’t slowed down by dumping energy into rifling – Spinning a properly stabilized bullet limits top rotation speed due to flywheel tress.
 
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Bart B.

New member
Yes, hoop stress.

First bad one in the shooting industry was shooting Sierra 28 caliber 168 grain match bullets in 7mm Remington Mag barrels. High velocity thin copper jacket bullets well over 3000 fps in 1:9 twist barrels. Obermeyer 5R rifled barrels helped a bunch until Sierra got better copper.

A year later, Sierra sent half a lot of 30 caliber 168 grain match bullets to the Army rifle team and the other half to the Navy team. Both teams had bullets flying apart before the 50 yard line shot from 7.62 NATO service rifles with maximum loads. The Army International shooting them in 308 Winchester reduced loads in free rifles used in 300 meter international matches said they were the most accurate bullets ever.

Navy got their bullets replaced, Army Int'l team kept all of theirs.
 
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TX Nimrod

New member
As stated by others above (years ago!) the solution to centripetal force is a solid copper bullet. Commonly available today, they could be designed to perform well at extreme terminal velocities. But other than an interesting mental exercise - who really cares?



.
 
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Double K

New member
One of my friends who was an engineer at Martin Marietta did some experiments with a 17 Remington to see how fast he could push a bullet.
He got over 7,000fps using bullets he turned from solid copper using duplex loads, he also drilled the barrel out removing the rifling.
 
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stuckinthe60s

New member
one would think accuracy and dependability would outweigh the need for speed. why so much desire for speed in todays ballistic world? just a novices' question.
 
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Double K

New member
It's human nature to experiment and push boundaries in everything around us, some people are less curious than others about what is possible and isn't.
To me that was a waste for my engineer friend to ruin that 700bdl{he eventually ruined the action as well} but it was his gun to do with as he pleased.
 
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Hal

New member
one would think accuracy and dependability would outweigh the need for speed. why so much desire for speed in todays ballistic world? just a novices' question.
Click to expand...
On the practical side - increased velocity delivers more potential distance & flattens out the trajectory.

On the not so practical side - "Hold my beer and watch this" and/or "look what I can do"...
 
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Ricklin

New member
Your old time engineer friend might want to broaden their knowledge base. The high speed dental turbine handpiece routinely turns at 400 thousand RPM, some go as high as 500 Thousand RPM.
They tend to be "all" RPM and "no" torque. With a diamond cutting instrument I know of no material that can't be cut.
The newer electric high speed handpiece attains a max. of 200 thousand RPM, Hand pressure alone will not stall the cutting instrument. It will cause the cutting instrument (bur) to fail violently. Yes, you can put out an eye with one.
My engineers loved the fact I had one. Perfect tool to modify a production mold they screwed up on. A diamond in a high speed handpiece did the trick.

Handy tip. Diamonds are cheap nowadays. One can purchase a chuck for Dremel or Foredom tools for dental size diamond burs. The variety of shapes and sizes is amazing. The burs are available under a dollar each. I modified the Borosilicate glass print bed for my 3d printer, quick and easy with a diamond.
 
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Double K

New member
Ricklin said:
Your old time engineer friend might want to broaden their knowledge base. The high speed dental turbine handpiece routinely turns at 400 thousand RPM, some go as high as 500 Thousand RPM.
They tend to be "all" RPM and "no" torque. With a diamond cutting instrument I know of no material that can't be cut.
The newer electric high speed handpiece attains a max. of 200 thousand RPM, Hand pressure alone will not stall the cutting instrument. It will cause the cutting instrument (bur) to fail violently. Yes, you can put out an eye with one.
My engineers loved the fact I had one. Perfect tool to modify a production mold they screwed up on. A diamond in a high speed handpiece did the trick.

Handy tip. Diamonds are cheap nowadays. One can purchase a chuck for Dremel or Foredom tools for dental size diamond burs. The variety of shapes and sizes is amazing. The burs are available under a dollar each. I modified the Borosilicate glass print bed for my 3d printer, quick and easy with a diamond.
Click to expand...
Probably should have mentioned that was in 1978, technology has changed a good bit since then.
 
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Ricklin

New member
Way before that

The high speed turbine handpiece was invented in the early 60's, may have even been a touch earlier. It's not new technology by any measure.

What is fairly new is the lower cost of diamonds. High quality diamond burs (the cutter) used to cost 5 bucks each. They are now about one dollar each.
 
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TRX

New member
> Yep. Never tried them but some people said they shot as well as the rifle in question would shoot normal ammo.
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That turned out to be highly variable. Remington developed their .30-06 and .308 saboted rounds with normal production Remington rifle barrels; .002-.003 deep rifling with 1:10 twist. Unfortunately the rest of the industry was moving to slightly shallower rifling (jackets were getting harder and thicker for some hunting rounds) and they were backing off to 1:12 or even 1:14 twist to stabilize the lighter, pointier bullets that were becoming popular. On those rifles, the sabots would sometimes strip instead of spinning the bullet, and the slower twists didn't stabilize them enough for best accuracy.

That's why you see so many head-butting contests polarized at "I used them and they were great!" and "I used them and they shot like corkscrews!"

Remington also made the Accelerator for the .30-30. Twists and groove depth are all over the place on those, but I don't think they sold very many.

The Accelerators have been out of production for quite some time now, but if you want to give the idea a try, EABCO sells their own design of plastic sabots and a special bullet seating tool for quite reasonable prices. They also have loading data. Remington's .30-06 loads had 55 grain bullets at >4000fps, solid .220 Swift territory.
 
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Grey_Lion

New member
Navy has been playing with rail guns but reading some of their initial results indicates that they go through launch tubes like crazy as they wear out.

I'm aware that some conventional different results might be had with solid copper projectiles that behave differently under extreme pressures than FMJ rounds so that might lead you in a different direction in your research.
 
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TXAZ

New member
If a rail gun is fair game, then consider the ion thruster / ion gun, ant an electron gun found in older CRT-based TV’s.
https://www.nasa.gov/centers/glenn/technology/Ion_Propulsion1.html

NASA says …” often used just one at a time. Spacecraft powered by these thrusters can reach speeds up to 90,000 meters per second (over 200,000 mph). In comparison, the Space Shuttles can reach speeds around 18,000 mph.”
The muzzle velocity of the ions coming out (in a vacuum, in space or on a test rig on earth) is on the order of the speed of light, 300,000 Km/sec).


Conversely, you can build your own “Electron gun” (or pull it out of an old TV tube) and reach speeds over 13 million mph.
And this gun can kill if pointed at a very close target for extended periods of time).

“For an electron gun with a voltage between its cathode and anode of V = 100V the electron will have a speed of about v = 6 × 10^6 m/s.”
https://spark.iop.org › speed-electrons
The speed of electrons | IOPSpark - Institute of Physics
 
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Ricklin

New member
Very cool

Professionally I am a Radiology guy.
One of the darn few new products that still employ a vacuum tube. X-ray generators, radar, and microwave ovens are the only common items I can think of, I'm sure there are others.

High voltage required, 45,000 - 120,000 volts on the anode for human diagnostics.
I'm a careful sort, that kind of voltage can make you a pile of ashes. I'm old, not bold.
186,282 miles per second in a vacuum, the ballpark speed of light. Classic physics. Einstein.

That may or may not be the "real" speed limit of the universe, stay tuned!
 
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mrmeval

New member
I worked with a friend in the 90s. He worked up some max loads for .30-06. In one test the bullets never got to the chronograph. So we set up some paper targets facing each other to see where they were dying as he suspected they were disintegrating from the rotation or had terrible accuracy.

They were disintegrating, they peppered the paper at a few feet before the chronograph. The previous loading had hit 4k in a .30-06 with poor accuracy.

In another test a non-Remington .30 cal sabot for .22 bullet was used with a 5.56 bullet pulled from a old cartridges. This was loaded in a .308 and it did well on speed at about 4200 but accuracy was poor till he dropped the FPS down to around 3800. Accuracy was meager but close to a bolt action .223 rifle.
 
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