New Berger twist rate reccomendataions

[barefooter56]

http://www.bergerbullets.com/berger-bullets-twist-rate-recommendations-by-eric-stecker-bryan-litz/
This is Eric's article in the latest Berger Bullet Blog. These Optimum twist rates are based on a worse case scenario of 59 degrees Fahrenheit at sea level. Please go to our twist rate calculator to see what twist rate is best for you. Be sure to enter the correct or as close to correct altitude you will be shooting at. If you shoot at multiple altitudes use the lowest to get the correct twist rate for your application.

 

[Sheldon N]

Thanks Phil. To clarify, the recommendations output by the twist rate calculator haven't changed, this is just about the recommended twist listed on the box and data sheets?


Another follow up question, somewhat related.... Is the data output by the twist rate calculator valid for determining what velocity the bullet becomes unstable downrange? For example, I put in my cartridge/rifle info and I know that I get a stability factor of 1.54 at my muzzle velocity. However at my 500 yard velocity I'm down to 1.41 marginally stable, and at 1000 yards velocity it's down to 1.28 with degraded BC performance, then eventually becoming unstable. I'm assuming this is typical of all bullets and ballistic performance.

Does this info correspond with the when I should actually see the bullet start becoming unstable at extended range shooting?

 

[barefooter56]

Thanks Phil. To clarify, the recommendations output by the twist rate calculator haven't changed, this is just about the recommended twist listed on the box and data sheets?


Another follow up question, somewhat related.... Is the data output by the twist rate calculator valid for determining what velocity the bullet becomes unstable downrange? For example, I put in my cartridge/rifle info and I know that I get a stability factor of 1.54 at my muzzle velocity. However at my 500 yard velocity I'm down to 1.41 marginally stable, and at 1000 yards velocity it's down to 1.28 with degraded BC performance, then eventually becoming unstable. I'm assuming this is typical of all bullets and ballistic performance.

Does this info correspond with the when I should actually see the bullet start becoming unstable at extended range shooting?

Sheldon N,
The twist rate calculator is still correct. This is just about the data sheet ( which has been upgraded on our site) and the information on the box. In short, run your data entering the correct or as close to correct altitude you will be shooting at to check what you need . The new OPTIMAL twist rate is based on a worst case scenario of 59 degrees at sea level. If you are at a higher altitude the OPTIMAL twist rate will be different due to external factors. As for the second question you are correct but the added spin rate adds rotational stability to that helps as the bullet enters the trans and subsonic speeds.

 

[SteveOak]

.........However at my 500 yard velocity I'm down to 1.41 marginally stable, and at 1000 yards velocity it's down to 1.28 with degraded BC performance........?

How are you determining the stability downrange?

It would be incorrect to assume that the rotational rate of the bullet decreases proportionally with the decrease in velocity. The forces that cause the forward speed bullet to slow are many times greater than whatever forces may cause the rotational speed to slow.

 

[Sheldon N]

I was assuming that the rotational speed remained constant (though I doubt it does) and was just changing the velocity in the calculator to match what my drop charts show. The general principle being that slower bullets need more spin to remain stable, so as the bullet slows the stability and the BC degrade.

I was just curious if the twist rate calculator could be used to give some insight into how a bullet might perform as it slowed down. I would imagine that there are also other factors that affect transonic performance beyond just twist rate.

 

[SteveOak]

You are correct that the rotational speed of the bullet remains fairly constant for the typical duration of flight.

If you run the calculation at a lower velocity it would calculate a rotational speed based on the lower velocity times barrel twist and a new (lower) stability factor based on the (lower) rotational speed.

 

[dkhunt14]

I believe that if the bullet is stable it stays that way better downrange then if it is not as stable to start out. I believe that is why some guns seem to defy conditions and shoot through it better. Matt

 

[Sheldon N]

If you run the calculation at a lower velocity it would calculate a rotational speed based on the lower velocity times barrel twist and a new (lower) stability factor based on the (lower) rotational speed.

Ahhh, yes. That makes sense. Thanks for clarifying.

So the answer is NO, I can't use the twist rate calculator like I thought.