Is there a software that helps calculate bullet stability?

[DsGrouse]

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.

[GunnyGene]

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

[DsGrouse]

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

[GunnyGene]

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/

[DsGrouse]

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.


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


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.


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

Here it is finally under that 2.0 required for good stability.



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?

[GunnyGene]

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.

[DsGrouse]

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

[GunnyGene]

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.

[DsGrouse]

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.

[GunnyGene]

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.

[DsGrouse]

a response from JBM

Which stability calculator are you talking about? I don’t think the Miller stability formula is really applicable to pistol bullets - neither is Greenhill’s formula.

As for the McCoy calculation there are limits on the dimensions that the program checks.

Please see my comments below.

--
JBM Ballistics
jbm@jbmballistics.com

> 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.

Were they stable? If so, then no.

>
> 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.

Stable is stable.

> 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?

Never thought about it. I have never owned a carbine and probably won’t.

It’s not clear to me how the forces increase as the velocity increases. You have a higher force on the bullet due to the increased velocity and a higher stability due to the increased rotation. In rifle rounds, I typically see better stability at higher velocity so that tells me that the stability increases faster than the overturning force. I would expect that rifle bullets being longer (in general) would have a higher overturning force than pistol bullets so I would expect a faster pistol bullet to be more stable.

This is just me thinking out loud.

[GunnyGene]

I kind of expected they wouldn't have any specific info about pistol calibers, since ballistics is normally focused on long range performance (often over 500yds), and pistol ammo simply isn't effected to any significant degree by things like barrel whip, spin drift, and so on. But at least you got prompt reply.

One other thing I'll mention is the barrel length on your Henry. This was a topic that came up a couple years ago, and there was a lot of confusion about it. Henry used to measure barrel length from the muzzle to the forward end of the chamber, which meant that your 17.4" barrel is actually 16.4" long (approx) as seen by the bullet. They switched to the ATF method of barrel measurement a few years ago, which is from the muzzle to the closed bolt face, and presto your barrel became 17.4" long. This was convenient for the ATF, but if your concern is the actual length the bullet see's you need to use that shorter dimension, as it will make a difference in some ballistic calculations.

It makes sense if you think like a regulatory agency, since it allowed them to make a blanket rule that covers all rifles, pistols, and shotguns regardless of chamber length & caliber/gauge, but makes no sense if you think like a normal person who understands that what counts is what the bullet sees. The only exception to that rule is for revolvers, since the barrel of a revolver does not include an integral chamber.

[DsGrouse]

Most of my concern is for a stabilized bullet. I am shooting through a can 99% of the time. Most of those times i want the rounds to be subsonic. According to internet lore, some bullets don't stabilize well at subsonic speeds. Not wanting to blow baffles out of my can, I am trying to find the speeds i need to drive my given rounds at to be stable enough for suppressed shooting.

It seems like from JBM's response it isn't an issue as far as our pistol rounds go. As for barrel length, I was not too worried about that. The rate of twist was my concern. from the calculator's data, it showed a slower twist of 1:30 to 1:37 being the optimal twist given the constraints of the calculator.

Which is just that, a constraint. It wasn't designed for viewing pistol caliber stabilization. If i have time, I might rundown Miller, Mccoy and Greenhill to see if they have any additional thoughts on this as it relates to my interest of pistol rounds out of a carbine at subsonic velocities.