1/7 twist 53 grain flat base bullet

[762willdo]

The barrel diameter if resisting any rotation of the bullet so who’s to say once released of that restriction there isn’t a small increase of rotation before settling down to its slightly diminishing speed

 

[762willdo]

Simple physics.

So it’s theoretical…..

 

[mike mccormick]

How do you know…..

Mv ×12(inches per foot)× 60 (seconds per minute)= inches per minute. Divide by twist rate in inches, gives rotation per minute

 

[mike mccormick]

So it’s theoretical…..

Only if the rifling doesn't engrave the bullet

 

[762willdo]

This doesn’t look like the bullet is spinning at 36000 in the barrel

 

[RegionRat]

762willdo, the muzzle velocity to RPM for twist rate the guys have been showing you is correct.

What isn't as well known is the exact speed or RPM where any given bullet will come apart. There are many factors that affect this value but they are not hard to discuss.

Cup-Core bullets have individual designs and potential for defects. Barrels and their rifling are not all cut to the same designs and they can also have defects.

Even in a perfect spin test, there is often dispersion in the RMP limit to destruction.

Start adding in all those mentioned circumstances and the dispersion just gets wider. That said...

The best thing to do is ask the OEM what they know. Sometimes they can actually give you solid answers, and sometimes they can't.

 

[Murray Brook]

How do you know…..

How to Calculate Bullet RPM — Spin Rates and Stability « Daily Bulletin

Photo by Werner Mehl, www.kurzzeit.com, all rights reserved. Most serious shooters can tell you the muzzle velocity (MV) of their ammunition, based on measurements taken with a chronograph, or listed from a manufacturer's data sheet.

bulletin.accurateshooter.com

 

[rayporter]

my step son had a brand new 22 BR barrel that destroyed the brake when a bullet decided to come apart. he had less than 25 shots on the barrel.

 

[dcali]

It's not theoretical. It's geometry. That's like saying triangles are theoretical.

7" is way overkill for those bullets. like RegionRat said, it's tough to say when they'll come apart without trying. It will vary from barrel to barrel, and with a whole host of other variables.

 

[dcali]

This doesn’t look like the bullet is spinning at 36000 in the barrel
View attachment 1436308

It's closer to 300,000 than 36,000

 

[fkimble@charter.net]

The lead core heats up an melts. The high RPM causes the melted lead to exert pressure on the jacket. At some point the pressure in the jacket exceeds the jacket strength. Usually takes a little distance for the pressure to built up enough to let go. A nice smooth slightly used barrel doesn't have sharp lands to make deep scratches so may take longer to come apart since jacket is not compromised. A brand new barrel may have sharp edges still on the lands and make deeper cuts in the jacket weakening the jacket so a quicker poof, possibly just after exit. A well used barrel with a rough throat and or a carbon ring can create havoc with the jacket integrity. Various combinations including different jacket thickness's between brands and type bullets make it impossible to say when or if a bullet will come apart. But the faster the twist the sooner it will happen.

Was breaking in a new barrel with some left over varmit bullets, thin skinned Hornady SX'x. Had several not make it to the target. After a dozen rounds it stopped. I assume at that point the razor sharp edge on the lands had been wore off.

Frank