Range Report JBM and Stability

[Rarebreed93]

When the info is input into the JBM, Stability program.
What does that answer mean?


208 Amax
stability
1.194
What does the 1.194 stand for?
Is this the yards that the bullet will be stable?

 

[Fred_C_Dobbs]

Re: JBM and Stability

* Stability
Calculates the Miller stability factor. This formula was derived by Don Miller and published in Precision Shooting. This formula is much better than the antiquated Greenhill's formula. Stability value should be in the range of 1.3 to 2.0 to ensure bullet stability. Don Miller and Dave Brennan (editor of Precision Shooting) have also been kind enough to let me host his stability paper on my exterior ballistics bibliograpy page. The paper is titled A New Rule for Estimating Rifling Twist An Aid to Choosing Bullets and Rifles.

Source:
http://www.jbmballistics.com/ballistics/calculators/calculators.shtml

A New Rule for Estimating Rifling Twist An Aid to Choosing Bullets and Rifles

 

[Rarebreed93]

Re: JBM and Stability

Very good read, I understand.
The warmer it is the more stable the 208 Amax will become out of my 23.5" barrel w/ 1/12 twist.
(59.o degrees/29.92Hg)This is my base numbers.
So in 80 or 90 degree weather the bullet will become more stable.

 

[Trevor]

Re: JBM and Stability

Anything above 1.0 is considered stable; but ideally you want 1.4 SG to be able to shoot in all conditions among other things. I think JBM set out their parameters of 59oC and sea level 29.92hg you will need to punch in your numbers for your area. If you shoot colder then that (can't go below sea level) or slower then you Chrony muzzle velocity you will see a lower SG, below 1.0 and your going to have some interesting result. If I remember correctly the Army wants closer to 2.0 as they have to shoot in some adverse conditions.

Trevor

 

[Timo Turl]

Re: JBM and Stability

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rarebreed93</div><div class="ubbcode-body">When the info is input into the JBM, Stability program.
What does that answer mean?


208 Amax
stability
1.194
What does the 1.194 stand for?
Is this the yards that the bullet will be stable? </div></div>

1.194....what are you shooting ? If you are using a 308 24" 1:12 then to get stability over 1.15 you have to push the 208 north of 3,000 fps.

 

[MontanaMarine]

Re: JBM and Stability

It depends on your local conditions.

In current local conditions (temp 54F, pressure 25.41 Hg), I get a factor of 1.25, at 2600 fps in a 1/12 barrel.