Degrees of bullet stability

[roob]

G'day,

Of course for longer bullets you need a faster twist to stabilize them, we know this.

But... can faster twist barrels stabilize lighter bullets better than slower twists?

Example, say you've got a .243 and the following...
A 100gr bullet which needs 1:8 twist
A 70gr bullet which needs a 1:10 twist

The 100gr bullet wont shoot well in the 1:10 rifle, but the 70gr bullet will. Could the 1:8 twist rifle stabilize the 70gr bullet better than the 1:10 though?

I wondered if the faster twist barrel might stabilize the bullet over longer distances? or extreme distances?

Is there any difference? or as long as it's stable it's stable? And the flight of the 70gr bullet in both barrels would be the same?

[SendIt]

Possibly over a long enough distance... How that that is though I have no idea.

More likely I think the bullet would slow to subsonic speeds before then and the transition would throw it out anyway, before the twist became an issue.

That's just guess work TBH though...

[Lyam]

As I understand it they will destabilize over a long enough distance, but for 99% of shooters you'll have hit your target long before you reach that mark.

[Grated]

Are you struggling with some .243 loads in this specifically? Or is that just an example?

[roob]

No just an example.

I have a 7mm-08 and 22-250 myself, but I could remember a few weights and twist of the .243 of the top of my head was all

[5Tom]

There is the possibility of over-stabilizing the bullet which also negatively affects accuracy. Over stabilization is caused by faster twist rates for a given weight of bullet, such as your example of a 70gr projectile suited for a 1:10 twist and shooting it through a 1:8 twist barrel.

Think of those spinning jack things that you spin on a table. If you spin it too fast, it gets speed wobbles until the RPM eventually slows down. Once the jack reaches a certain range of RPM, you note that the jack spins extremely stable until the RPM drops below stability and begins to wobble again to the point it tips and stops.

Same can be said about projectiles and barrel rate of twists. Velocity also plays a major part too, hence why reloaders use chronographs to measure velocity. The rate of twist is fixed, therefore the amount of charge in gun powder will determine the velocity and determine RPM, which all falls in line to bullet stability at a given RPM.

[Apollo]

Everyone has an opinion, so here goes.

I do not believe it is possible to over-stabilize a bullet within reasonable circumstances.

The comparison of a bullet to a spinning jack in my view is a bad comparison. A spinning jack does just that, spin and nothing else so possibly yes it can be over stabalized and start to wobble out of control BUT a bullet does not just spin. A bullet has supersonic velocity forwards through the air and by the bullet's design this keeps it tracking forward in it's trajectory.

Another factor to consider is spin drift (not instability) that will cause a bullet to curve sideways in it's path over long distances and hence the trajectory is not perfectly straight.

Many ballistics experts have put forward their versions, the likes of Brian Litz has written a great deal on the subject of bullet stability.

The most likely problem with over-stabilizing a bullet to an extreme level is created by the bullet design or lack of it and poor manufacturing in that a grossly over spun bullet is more likely to fail in it's construction. Some say explode but it is more the fact that the centrifugal forces applied to the core cause it to expand and fracture the bullets jacket.

Loss of stability can occur from tail turbulance created by using the wrong bullet design or dropping into transonic flight. In general flat based bullets are more stable at short distances than boat tail bullets which are designed for long distance. Some boat tail bullets are known to take some distance before they become properly stable and this is not from spin rate but by the turbulance behind the bullet base (from behind the bullet).

As far as a .243W with a 1:10 twist rate I have used bullets of different designs from 55gr to 100gr in weight and all have been very accurate. There are some 100gr bullets by their own design that will not stabilize properly due to their length and the slow twist rate.

In my .223R with a 1:9 twist rate I have shot bullets as low as 30gr in weight and they have proven to be very accurate over reasonable distances. Wind drift being the biggest problem.

[roob]

I appreciate the opinion Apollo. And 5Tom, everyone else...

This isn't a problem for me, I just like to understand is why I'm asking.

The more info the better

[Warrigul]

I appreciate the opinion Apollo. And 5Tom, everyone else...

This isn't a problem for me, I just like to understand is why I'm asking.

The more info the better

Really over stabilisation isn't the biggest issue with twist rates, more that you want the least amount of twist neccesary to stabilise the projectiles you wish to use at the velocity you expect.

The less twist you have the less pressure and you can stoke them a bit harder for distance.

It is all a bit eye of newt and the sweat off a toads back at midnight stuff but if all you are going to do is use 55 grain projectiles then having a 1:7 capable of stabilising 80 grainers is just a waste.

[Old Fart]

It is all a bit eye of newt and the sweat off a toads back at midnight stuff but if all you are going to do is use 55 grain projectiles then having a 1:7 capable of stabilising 80 grainers is just a waste.

Yeah, worrying over nothing for the most part with this stuff I think.

Try a few different bullets, one will shoot well, keep using it.

[Aster]

I do not believe it is possible to over-stabilize a bullet within reasonable circumstances.

That's my opinion too.

It's one of these shooting theoretical's that people get caught up on that they're likely never to encounter.

Like you said, reasonable circumstances. I don't know any regular shooter that's had the problem.

IMO you need an aggressively fast twist (for the bullet) and to be pushing the envelope with velocities before it becomes a potential concern.

Just 2c.

[Wheelbarrow]

The more info the better

That's a good philosophy, especially in shooting.