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Is there a software that helps calculate bullet stability?

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DsGrouse
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Is there a software that helps calculate bullet stability?

Post by DsGrouse » Sat May 14, 2022 8:05 am

By that, well I suppose what I am looking to do is.

1 input weight of the bullet, bullet OAL, estimated speed, barrel rifling, and length and get an idea if the bullets will be stable.
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GunnyGene
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Re: Is there a software that helps calculate bullet stability?

Post by GunnyGene » Sat May 14, 2022 8:20 am

DsGrouse wrote:
Sat May 14, 2022 8:05 am
By that, well I suppose what I am looking to do is.

1 input weight of the bullet, bullet OAL, estimated speed, barrel rifling, and length and get an idea if the bullets will be stable.
Yes, there's a couple here that might help:

Modified Point Mass Trajectory, and Miller Stabiity factor.

https://www.jbmballistics.com/ballistic ... tors.shtml
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Re: Is there a software that helps calculate bullet stability?

Post by DsGrouse » Sat May 14, 2022 9:57 pm

It most of these bullets are over-stabilized? Am I missing something? I am coming up with stability rates around 5 to 7, when most recommend 1.5 to 2.0
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Re: Is there a software that helps calculate bullet stability?

Post by GunnyGene » Sun May 15, 2022 7:48 am

DsGrouse wrote:
Sat May 14, 2022 9:57 pm
It most of these bullets are over-stabilized? Am I missing something? I am coming up with stability rates around 5 to 7, when most recommend 1.5 to 2.0
Can't help with that. I'd guess that it's something to do with the inputs. JBM software is pretty well regarded, so not likely a calc glitch. You might try contacting them about it. There's a link to the email contact page in the JBM header.

Berger also has an online calc for this if you want to compare:

https://bergerbullets.com/twist-rate-calculator/
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Re: Is there a software that helps calculate bullet stability?

Post by DsGrouse » Sun May 15, 2022 8:31 am

I had a bunch of open tabs with bullet weights, sizes and velocities up last night. I was waiting to copy and past this morning. Fricken windows update. GRRRRR.

Here is a quick rundown using the JBM.
Specifics off henry's website.
Image

Both 45c, and 357/38 are listed as 1:16 inch twists. I never really thought much of it, but I did wonder if i was under-stabilizing my 158 grain bullets. As my 148grn's were much better performers.

Kind of sort of is the answer. The 158's I measured last night were in the 10's as far as the stability score. So I was wrong, It seems I am over-stabilizing if I am to go by this calculator.

148 grain bullets at 1:16
Image

Increasing the velocity up to 3000 fps increases the stability. Decreasing it down to lowest allowable at 500 fps does not change it from 6.591 The only thing that changes it is slowing the twist rate.

Same 148grn DEWC with a 1:30 twist.
Image

Here is the data for the 45 colt. Again i had more tabs open, more bullet weights and velocities along with different calculators. each with the same kind of result.
45colt 1:16 twist
Image
Here it is finally under that 2.0 required for good stability.

Image

What am I missing? Do pistol rounds at pistol velocities via a carbine require a different twist, and thus henry is right, or does the stability factor change when shooting pistol rounds at pistol velocities via carbine change?
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Re: Is there a software that helps calculate bullet stability?

Post by GunnyGene » Sun May 15, 2022 9:31 am

I think you might be misinterpreting the calculated stability number. The way I understand it, is that the minimum for acceptable stability is in the range of 1.5 to 2.0. Of course, you can spin the bullet so fast that it comes apart or has other ballistic problems, but I don't know what the upper limit is, or what the optimum is, relative to internal and external ballistics for a particular bullet/barrel. At some point other considerations probably come into play such as barrel leading, pressures, spin drift, etc. I'm feeling much of this is above my paygrade. :)

The Berger link seems to be a better representation of this stability business.
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Re: Is there a software that helps calculate bullet stability?

Post by DsGrouse » Sun May 15, 2022 9:48 am

I looked on the berger site, and one other last night, one of the two gave the comment that it was over-stabilized.

Yeah above my paygrade, but I like to know enough so that I can ask the right questions.

I am betting, that more than anything, this is my issue. I simply don't know enough
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Re: Is there a software that helps calculate bullet stability?

Post by GunnyGene » Sun May 15, 2022 10:31 am

DsGrouse wrote:
Sun May 15, 2022 9:48 am
I looked on the berger site, and one other last night, one of the two gave the comment that it was over stabilized.

Yeah above my pagrade, but i like to know enough so that i can ask the right questions.

I am betting, that more than anythis is my issue. I simply dont know enough

Just as a point of refernce, I ran the numbers (JBM) for my .41mag BBSC.

Stability
Input Data
Caliber: 0.410 in Bullet Weight: 210.0 gr
Bullet Length: 0.680 in Plastic Tip Length: 0.000 in
Muzzle Velocity: 1738.0 ft/s Barrel Twist: 18.0 in
Temperature: 59.0 °F Pressure: 29.92 in Hg
Output Data
Stability: 6.504

The cartridge I use is the Underwood 210grn XTP. Very accurate, and is my deer getter. Never had any concern about over stabilizing. Got the same result on the Berger calc.
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Re: Is there a software that helps calculate bullet stability?

Post by DsGrouse » Sun May 15, 2022 12:04 pm

GunnyGene wrote:
Sun May 15, 2022 10:31 am
DsGrouse wrote:
Sun May 15, 2022 9:48 am
I looked on the berger site, and one other last night, one of the two gave the comment that it was over stabilized.

Yeah above my pagrade, but i like to know enough so that i can ask the right questions.

I am betting, that more than anythis is my issue. I simply dont know enough

Just as a point of refernce, I ran the numbers (JBM) for my .41mag BBSC.

Stability
Input Data
Caliber: 0.410 in Bullet Weight: 210.0 gr
Bullet Length: 0.680 in Plastic Tip Length: 0.000 in
Muzzle Velocity: 1738.0 ft/s Barrel Twist: 18.0 in
Temperature: 59.0 °F Pressure: 29.92 in Hg
Output Data
Stability: 6.504

The cartridge I use is the Underwood 210grn XTP. Very accurate, and is my deer getter. Never had any concern about over stabilizing. Got the same result on the Berger calc.

Thank you, that is the kind of real world data that i was looking for. I have an email into JBM also. Maybe, they will shed some light on it.
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Re: Is there a software that helps calculate bullet stability?

Post by GunnyGene » Sun May 15, 2022 12:16 pm

DsGrouse wrote:
Sun May 15, 2022 12:04 pm
GunnyGene wrote:
Sun May 15, 2022 10:31 am
DsGrouse wrote:
Sun May 15, 2022 9:48 am
I looked on the berger site, and one other last night, one of the two gave the comment that it was over stabilized.

Yeah above my pagrade, but i like to know enough so that i can ask the right questions.

I am betting, that more than anythis is my issue. I simply dont know enough

Just as a point of refernce, I ran the numbers (JBM) for my .41mag BBSC.

Stability
Input Data
Caliber: 0.410 in Bullet Weight: 210.0 gr
Bullet Length: 0.680 in Plastic Tip Length: 0.000 in
Muzzle Velocity: 1738.0 ft/s Barrel Twist: 18.0 in
Temperature: 59.0 °F Pressure: 29.92 in Hg
Output Data
Stability: 6.504

The cartridge I use is the Underwood 210grn XTP. Very accurate, and is my deer getter. Never had any concern about over stabilizing. Got the same result on the Berger calc.

Thank you, that is the kind of real world data that i was looking for. I have an email into JBM also. Maybe, they will shed some light on it.
BTW, the MV (1738) is from my own chrono test a couple years ago and is the avg. of a 5rnd string.
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