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Is there a software that helps calculate bullet stability?

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DsGrouse
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Re: Is there a software that helps calculate bullet stability?

Post by DsGrouse » Sun May 15, 2022 4:23 pm

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.
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GunnyGene
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Re: Is there a software that helps calculate bullet stability?

Post by GunnyGene » Mon May 16, 2022 9:09 am

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.
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DsGrouse
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Re: Is there a software that helps calculate bullet stability?

Post by DsGrouse » Mon May 16, 2022 9:44 am

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.
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