Speaking of spinning bullets....

[Hardpan Curmudgeon SASS #8967]

Not to mess with @Buckshot Bear's "spinning ice bullet" thread, but....

 

Have any of y'all ever wondered or given an idle thought to how fast bullets really do spin? 

 

Danged fast, that's how fast! 

 

Here's the formula.... 

 

A bullet that matches the rifling of the firing barrel will exit that barrel with a spin:

S=υ0Lwhere υ0 is the muzzle velocity and L is the twist rate.

For example, an M4 Carbine with a twist rate of 1 in 7 inches (177.8 mm) and a muzzle velocity of 3,050 feet per second (930 m/s) will give the bullet a spin of 930 m/s / 0.1778 m = 5.2 kHz (314,000 rpm).

 

I don't care who ya are, three-hundred-fourteen-thousand RPM's is danged fast!  

 

Evidently, improperly designed bullets have been known to disintegrate in flight due to centrifugal force.  

 

                           

 

[Michigan Slim]

I made up a bunch of Hornady Vmax loads. One or two in ten never make the target. You can see in the snow where they just blow apart. This is out of my Colt Match Target HBAR. 

[Hardpan Curmudgeon SASS #8967]

1 hour ago, Michigan Slim said:

I made up a bunch of Hornady Vmax loads. One or two in ten never make the target. You can see in the snow where they just blow apart. This is out of my Colt Match Target HBAR. 

 

Slim, do you know your muzzle velocity?  Does it have the 1/7 rate of twist barrel?  

[Choctaw Jack]

I used to use a 220 Swift for Prairie dogs, great rifle in a great caliber.

Bought a new ( to me ) brand of bullets, and they were like shooting a .22 shotshell. Maybe one in 5 or 6 impacted as a whole bullet.

After a little research ( I read the label) , I found that these projectiles were designed for velocities under 3000fps.

I was pushing them at around 3800 .

Centrifugal force was exploding them mid-flight.

Rpm was approximately 330,000 at that speed!

[Michigan Slim]

8 hours ago, Hardpan Curmudgeon SASS #8967 said:

 

Slim, do you know your muzzle velocity?  Does it have the 1/7 rate of twist barrel?  

1:7 twist. Unsure of the exact MV but it is listed at 2950ish in my manual. 20" barrel also. 

[bgavin]

Wow.
I do know that  Hornady has an upper velocity limit on their XTP bullets.
This limit becomes problematic when shooting hand gun XTP in rifles.

H110/296 really pushes these bullets in a rifle application.