Doug Huffman wrote:
Bullets can spin upwards of 300,000 RPM +
for rifle bullets, not sure about pistol bullets.
Sorry, that just doesn't sound right.
Twist is expressed as 'one in ten inches' for instance. Just doing an order of magnitude estimate gives 10, 000 rpm
. One twist in a ten inch barrel. The bullet takes a millisecond at a thousand feet per second to travel the ten inch barrel and acquire its angular momentum.
Further, and for this I have no 'formula' in my head, I doubt lead and likely steel would withstand the centripetal forces of 300,000 rpm and would disintegrate.
Lead yield strength is 12 MPa Alloy 514 yield strength is 760 MPa. '10^4 sec^-1' and '3 x 10^5 sec^-1'. R = 0.5 cm.
OK. Let's take a common rifle bullet:
223 Remington (5.56x45mm) -- 62 gr FMJ (steel core), 3020 fps, 1255 ftlbs
We'll figure it fora barrel with a 1 in 12" Twist first to make the math easier.
1 twist per foot, x 3020 Feet per Second = 3020 Revolutions Per Second.
3020 x 60 (seconds per minute) = 181,200 RPM.
A 1 in 7" Twist (not uncommon for a .223 barrel) would push that same bullet to over 310,000 RPM.
I had no idea bullets spun at such a high RPM either, until I read John Ross's Unintended Consequences
(I can't recommend that book enough). Fictional novel, but a lot of factual informationthrown in. One character has a custom varmint rifle that does have such a high twist and high velocity that about 1 in 10 bullets DOES just desintegrate mid-air.