Margnal twist rate stabilizing question

[Yippeekiay]

I have a 23" 300wm barrel with a 1/12 twist rate that was designed for lighter (135 gr) bullets. I'd like to run 185's but calculators say it wouldn't stabilize properly.
I'm wondering if there's is a specific distance, say 300 yards, that is used in this determination. So the bullet might just stabilize if it had longer to go.
Wishful thinking.

 

[_Windrider_]

I have a 23" 300wm barrel with a 1/12 twist rate that was designed for lighter (135 gr) bullets. I'd like to run 185's but calculators say it wouldn't stabilize properly.
I'm wondering if there's is a specific distance, say 300 yards, that is used in this determination. So the bullet might just stabilize if it had longer to go.
Wishful thinking.

I don’t know if it’s necessarily the twist rate that’s the issue, but it might be the length of the barrel not getting enough velocity for the bullet to stabilize

 

[Yippeekiay]

Possibly.
I guess the root of the question is if a marginal bullet will eventually stabilize. Hard to imagine a 300wm lacking velocity.

 

[Aftermath]

No projectile ever becomes more stable at distance...exception is an arrow/bolt/dart that is flexing as it gets launched.

As velocity fades, as the rotation (that is induced by the twist) fades, so does stabilization. You can always shoot that round and determine if the stabilization is good enough to meet your needs. By that I mean if the "cone" (1? 2? 3? MOA) that bullet will arrive at target is within your acceptable tolerance for your desired use.

Personally, I'd just have a barrel with a more appropriate twist installed.

 

[Yippeekiay]

Yeah. Best thing is to try em and if they don't shoot go with the proven lighter bullet. I just have a bunch of Juggernauts and don't wanna waste them.

 

[Aftermath]

I mean...you could use this to convince she who must be obeyed that there is a viable need for another bullet launcher...

 

[Yippeekiay]

She would actually be ok with that. I just couldn't pass up such a good deal on a phat barrel.

 

[Ledzep]

No projectile ever becomes more stable at distance...exception is an arrow/bolt/dart that is flexing as it gets launched.

As velocity fades, as the rotation (that is induced by the twist) fades, so does stabilization. You can always shoot that round and determine if the stabilization is good enough to meet your needs. By that I mean if the "cone" (1? 2? 3? MOA) that bullet will arrive at target is within your acceptable tolerance for your desired use.

Personally, I'd just have a barrel with a more appropriate twist installed.

Not really accurate.

Rotation degrades much slower than linear velocity and if you do 4DoF or 6DoF calculations on stable projectiles you'll see that SG actually increases downrange until you're several seconds into the flight at which point magnus usually starts upsetting things.

This is true even if the muzzle exit SG is below 1.0. However, there are AoA bounds that govern whether a bullet will fall back into point-forward flight if it is for whatever reason destabilized (or never started stable) then climbs back up to >1.0 SG. Theoretically you can launch a bullet unstable at high velocity and have it snap back point-forward down range after the frontal airflow slows down, but usually in those borderline cases the damage from the initial high AoA flight has already been done on the dispersion side of things by the time it settles back in.

 

[Aftermath]

Not really accurate.

Rotation degrades much slower than linear velocity and if you do 4DoF or 6DoF calculations on stable projectiles you'll see that SG actually increases downrange until you're several seconds into the flight at which point magnus usually starts upsetting things.

This is true even if the muzzle exit SG is below 1.0. However, there are AoA bounds that govern whether a bullet will fall back into point-forward flight if it is for whatever reason destabilized (or never started stable) then climbs back up to >1.0 SG. Theoretically you can launch a bullet unstable at high velocity and have it snap back point-forward down range after the frontal airflow slows down, but usually in those borderline cases the damage from the initial high AoA flight has already been done on the dispersion side of things by the time it settles back in.

So....are you saying that as the rotation slows and as the linear velocity slows, stability is degraded?

 

[Aftermath]

Not really accurate.

Rotation degrades much slower than linear velocity and if you do 4DoF or 6DoF calculations on stable projectiles you'll see that SG actually increases downrange until you're several seconds into the flight at which point magnus usually starts upsetting things.

This is true even if the muzzle exit SG is below 1.0. However, there are AoA bounds that govern whether a bullet will fall back into point-forward flight if it is for whatever reason destabilized (or never started stable) then climbs back up to >1.0 SG. Theoretically you can launch a bullet unstable at high velocity and have it snap back point-forward down range after the frontal airflow slows down, but usually in those borderline cases the damage from the initial high AoA flight has already been done on the dispersion side of things by the time it settles back in.

Also, in the application as presented by OP, would you predict that projectile to become more stable as it travels towards some impact point?

 

[Ledzep]

So....are you saying that as the rotation slows and as the linear velocity slows, stability is degraded?

The linear velocity slows at a faster rate than the rotational velocity as the bullet goes down range. It effectively behaves as if the twist rate was increased as the bullet goes down range and SG increases the entire flight.

Also, in the application as presented by OP, would you predict that projectile to become more stable as it travels towards some impact point?

Gyroscopic stability will increase through the entire flight path, however dynamic stability may not. SG will keep going up but if it's never able to "hand off" from gyroscopically stable to being dynamically stable, the bullet will remain in a funky AoA state.

 

[Yippeekiay]

So no good groups down range even if the bullet did stabilize..
Bummer

 

[Ledzep]

So no good groups down range even if the bullet did stabilize..
Bummer

Yeah usually below 1.1 is a gamble if it will stay point-forward at all. 1.0-1.2 will often suffer with dispersion, and 1.2-1.4 will have good dispersion (usually) with a slight hit to total drag. My personal cutoff for even trying it out is 1.2-1.25. Below that I've had rare success.

 

[DocUSMCRetired]

You reduce the BC by around 3% for every 0.1 loss in SG. So with a 1.2 I wouldn't call that marginal. That's a possible 9% decrease in performance.