Berger Twist Rate Stability Calculator (need help)

[Bill Norton]

Hi all,
I'm about to order a new barrel for my Blaser R8 and I have decided on a 6.5-280ai. I have a few bullets in mind and I ran the calculations through the Berger Twist Rate Stability Calculator and it says a 1:7 is very stable. My question is the Berger calculator pretty accurate? Hornady says a MINIMUM of 1:8 is needed for the 143 ELD-X but the calculator says something different so I guess I'm confused... Thanks in advanced!

Hornady 143gr ELD-X
1:7

Hornady 143gr ELD-X
1:8

Berger 140 VLD
1:7

Berger 156 Elite Hunter 1:7

 

[jebel]

The Berger twist calculator works fine, but it does not include a variable for polymer tipped bullets (Berger doesn't sell any). The polymer tip affects the calculation. Generally the Berger calculator will overestimate the twist necessary to stabilize bullets with polymer tips.

For Hornady ELD-X bullets (polymer tip), use the JBM calculator.

JBM - Calculations - Stability

www.jbmballistics.com

If you need to know the length of the polymer tip itself, measure it or use the JBM bullet length list.

JBM - Bullet Length List

www.jbmballistics.com

An SG value of 1.5+ at sea level conditions is generally considered fully stabilized. There is some debate over how high you want to go with the SG value, which you can research on this website or ask about.

 

[jebel]

I just re-read your initial post. Is it possible you're confusing twist rates? 1:7 is a faster twist rate than 1:8. No offense intended.

It might help if you clarify what you need. Are you asking what is the slowest twist rate you can have to stabilize (SG 1.5+) the Hornady 143 gr ELD-X in a 6.5-280ai?

 

[Tiny Tim]

Each of those shown are fully stabilized. Hornady simply states on their box the minimum recommended twist. Velocity, twist rate, and environmental factors (altitude, temp ...) all affect this. Jebel's recommendation of JBM calculator is spot on for tipped bullets as well. Not sure if you did the calculation for an 8 twist with the 156. that might be close, but for all the others, an eight twist will serve you well.

 

[lancetkenyon]

Minimum and "optimal" are not the same thing. I would go 1:7.5" if I were you. If you can't find a 1:7.5", then 1:7". Especially for the 156.
Berger used to put "optimal" twist rates on their boxes. Now they put "minimum" to sell more bullets.

 

[L.Sherm]

Here's something off of Randy Robinetts website of Bib Bullets he has on there and I'm a firm believer in also.

 

[P7M13]

And if you plan on shooting monos, look at JBM like @jebel recommends.
Have also shot monos in my 7-08 that calculate as "marginally stable" and gotten the best accuracy out of the rifle, ever. Go figure....

 

[L.Sherm]

I can tell you also I know of people who have had bullets not make it to the target with bullets of an SG over 2.0 .
Its something that seems to happen as you get rounds down a barrel and throat wear, i believe there was a thread a few days ago about a guy with a 28 Nosler that had 500 rounds on a barrel that sounded like thats what his problem was.

 

[Bill Norton]

I just re-read your initial post. Is it possible you're confusing twist rates? 1:7 is a faster twist rate than 1:8. No offense intended.

It might help if you clarify what you need. Are you asking what is the slowest twist rate you can have to stabilize (SG 1.5+) the Hornady 143 gr ELD-X in a 6.5-280ai?

Thanks for your help. Twist rates are confusing to me.

Hornady says it needs a minimum of 1:8. Does this mean 1:7 falls within it? Sorry for the stupid question, I just want to make sure before I drop the cash.

 

[Bill Norton]

I just re-read your initial post. Is it possible you're confusing twist rates? 1:7 is a faster twist rate than 1:8. No offense intended.

It might help if you clarify what you need. Are you asking what is the slowest twist rate you can have to stabilize (SG 1.5+) the Hornady 143 gr ELD-X in a 6.5-280ai?

Im looking for the best twist rate for this or the berger 140 vld

 

[Tiny Tim]

No stupid questions exist. 1 in 7 means 1 complete revolution of the bullet in 7 inches of barrel. 1 in 8 means 1 complete revolution in 8 inches. Therefore, a 7 twist is faster and will impart more spin or "stability' to the bullet. This not only affects accuracy but can also affect terminal performance. As previously pointed out, a SG of 1.4-1.9 seems to strike the best balance.

 

[Hugnot]

The JBM stability estimator matches my Miller stability estimator that has been modified for plastic tipped bullets. The JBM estimator allows entry of plastic tip lengths. The Miller calculations are only estimates of expected stability. The Berger calculations are similar. I successfully modified the Miller calculation to work off-line using the Open Office spread sheet, it provides identical results as the JBM.

Apparently, Hornady uses their 4DOF calculations to derive optimum twist rates. A description of the method is provided on the Hornady site (better them than me).

Two different methods. Search for a copy of the Miller EXCEL calculation on-line then see how it works on EXCEL. Get into the Hornady site with its method description.

I use the Miller and Hornady methods before buying bullets or getting new rifle barrels.

 

[Bill Norton]

No stupid questions exist. 1 in 7 means 1 complete revolution of the bullet in 7 inches of barrel. 1 in 8 means 1 complete revolution in 8 inches. Therefore, a 7 twist is faster and will impart more spin or "stability' to the bullet. This not only affects accuracy but can also affect terminal performance. As previously pointed out, a SG of 1.4-1.9 seems to strike the best balance.

Thank you. If it is greater that 1.9 is it more stable or less?

 

[L.Sherm]

If you wanna run 140 - 150 class bullets go with 1-8.