Round ball verses conical

[coloradoclyde]

Exactly... :thumbsup:
The score is now;
3 understand
1 does not.

 

[Gene L]

So you're saying, Gus, that the rotation of a bullet picks up speed after it leaves the bore?

That's kinda like the guy who thought a bullet speeds up 10 feet from the muzzle.

A Gyro-Jet, yes. A bullet, no. Bullets slow down as soon as they leave the muzzle. And they begin to drop. They drop at the same rate no matter what the forward velocity, gravity being what it is. And I suspect they lose rotation at a given rate.

The example you gave with the football illustrates why a faster twist stabilizes a bullet better. The velocity may be greater, but so is the twist applied to it. So the QB is shooting from a fast-twist arm.

Same with the drill. When you push it faster, you in essence speed up the twist and it gains velocity.

Following the majority opinion on this discussion, speeding up the velocity actually decreases RPM, since the time of flight is significantly less with a higher velocity.

As it stands, a typical rotational speed is around 230,000 RPM, but M is not an accurate statistic, since only in artillery do projectiles travel a full minute.

 

[coloradoclyde]

The point I was making is something is either stable or unstable. No such thing as "over stabilized."

Both velocity and rotation contribute to stabilization...
To much or not enough velocity and the bullet will not stabilize.
The same goes for rotation, spin, twist, RPM or whatever you want to call it.
As velocity increases, so does Rpm
RPM is just a unit of measurement and it doesn't matter that the bullet may not be in flight for a full minute.
It's like traveling in your car at 50 MPH but you only drove it for 30 minutes......that has no impact on the car's aerodynamics.
Speed does.....but the length of time you drove doesn't.......un less your car runs out of gas or experiences some other force.

 

[coloradoclyde]

So you're saying, Gus, that the rotation of a bullet picks up speed after it leaves the bore?

NO!
And no one said that......but that's what you are thinking and that is the problem....
From the moment the bullet leaves the barrel everything is slowing down.... Velocty, rotation etc....
But I think the point you are missing is that....once the powder is ignited everything is accelerating up to the point where it leaves the barrel....It's the time component that you keep leaving out....

 

[Artificer]

So you're saying, Gus, that the rotation of a bullet picks up speed after it leaves the bore?

No, I am not saying that.

A bullet does pick up speed INSIDE a bore up to a certain length of barrel, but not after it leaves the bore. From the time the bullet leaves a bore, it is slowing down because there is no more gas pressure acting against it.

What I am saying is that the rifling causes the spin, but also restricts how much it can spin while the ball is inside the bore.

AFTER the ball leaves the bore, rate of rotation/spin is no longer controlled (or held back) by the friction/drag of the rifling. Since there is no drag from the rifling after the ball leaves the barrel, the ball will spin faster with a greater powder charge than it does when the powder charge is smaller - even though in both cases of a lesser or larger powder charge, the ball slows down once there is no more gas pressure pushing it, after it leaves the barrel.

Gus

 

[Gene L]

So you're saying, Gus, that the rotation of a bullet picks up speed after it leaves the bore?

NO!
And no one said that......but that's what you are thinking and that is the problem....
From the moment the bullet leaves the barrel everything is slowing down.... Velocty, rotation etc....
But I think the point you are missing is that....once the powder is ignited everything is accelerating up to the point where it leaves the barrel....It's the time component that you keep leaving out....

I agree with most of that. With some exceptions:

The time component in the barrel must be measured in millions of a second. The ToF (Time of Flight) is easily measured, my Speer loading manual has pages of ToF measures. Based on velocity and BC...Ballistic Coefficient. A round ball has an awful BC.

Twist is set in the barrel and is independent of initial velocity. Since nothing speeds up when it leaves the bore, it only follows that the velocity and RPM must slow down. The RPM more slowly because it starts off more slowly compared to forward velocity.

I simply can't understand any argument for velocity affecting RPM. Given that, a 12-twist (I only use 12 twist because it's easier to figure out) a 12 twist will rotate a bullet 300 times in 100 yards. If you go back to the first edit I made, read the first sentence of that edit. It basically says the same thing. As do many others. Don't take my word for it, google it.

As has been noted, perhaps a few times to many, I'm new to this forum, but I hope it's not one of those forums where one gains ascendancy through simply posting a lot. If that is the unfortunate case, I'm afraid I'm way behind you guys with several hundred posts.

 

[coloradoclyde]

The time component in the barrel must be measured in millions of a second.

Why?


And, we are not discussing time of flight as a separate thing...

Try sticking to one subject.....

 

[Artificer]

The example you gave with the football illustrates why a faster twist stabilizes a bullet better. The velocity may be greater, but so is the twist applied to it. So the QB is shooting from a fast-twist arm.

Have to admit I do not follow your reasoning on this. There is only so much twist or spin the hand can put on a football, no matter how much force is used to throw a ball.

But what the football example does show is when more force is applied to the football, it will spin faster and go farther after it leaves the Player's hand than it did with a softer throw. This mimics the external ballistics in a rifle.

Gus

 

[coloradoclyde]

I simply can't understand any argument for velocity affecting RPM.

Yes, we've noticed.....
Go outside and throw a football for a couple of hours and watch it spin while changing the velocity.
You'll have an epiphany.....

 

[Gene L]

The example you gave with the football illustrates why a faster twist stabilizes a bullet better. The velocity may be greater, but so is the twist applied to it. So the QB is shooting from a fast-twist arm.

Have to admit I do not follow your reasoning on this. There is only so much twist or spin the hand can put on a football, no matter how much force is used to throw a ball.

But what the football example does show is when more force is applied to the football, it will spin faster and go farther after it leaves the Player's hand than it did with a softer throw. This mimics the external ballistics in a rifle.

Gus

And only so much spin you can put on a bullet. Limited by the twist of the barrel. The range of possibilities on either a football or a bullet are limited. They are not infinite.

 

[Dean2]

So you're saying, Gus, that the rotation of a bullet picks up speed after it leaves the bore?

That's kinda like the guy who thought a bullet speeds up 10 feet from the muzzle.

A Gyro-Jet, yes. A bullet, no. Bullets slow down as soon as they leave the muzzle. And they begin to drop. They drop at the same rate no matter what the forward velocity, gravity being what it is. And I suspect they lose rotation at a given rate.

The example you gave with the football illustrates why a faster twist stabilizes a bullet better. The velocity may be greater, but so is the twist applied to it. So the QB is shooting from a fast-twist arm.

Same with the drill. When you push it faster, you in essence speed up the twist and it gains velocity.

Following the majority opinion on this discussion, speeding up the velocity actually decreases RPM, since the time of flight is significantly less with a higher velocity.

As it stands, a typical rotational speed is around 230,000 RPM, but M is not an accurate statistic, since only in artillery do projectiles travel a full minute.

Gene

I am not trying to pile on here, but your understanding of twist rate and its affect on bullets is WRONG. Velocity does in fact affect the RPM of a bullet, even with the same twist barrel.

A 1/25 twist may not stabilize a particular conical at 1000 fps, but will stabilize it just fine at 1500 fps, because you have increased the RPM sufficiently to stabilize the bullet.

You are correct that a 1/12 twist rotates the bullet once in 12" while in the barrel. Once free of the barrel, that bullet, travelling at 1000 fps, means the bullet having travelled 1000 feet, or 333.3 yards, will have rotated 1000x in that second. That makes its rotational speed 12,000 rotations in one second. If the muzzle velocity is 2000 fps, your rotational speed would be 1000 feet in 1/2 second x 12 or 24,000 rotations per second.

The part I think you are forgetting is time in barrel: at 1000 fps, with a 12" barrel, the bullet is in the barrel .012 of a second. At 2000 fps, it is in the same barrel 1/2 the time or .006 of a second. Therefore the bullet only turned once in the 12" but in these two cases it did it in literally half the time. That rate of rotation remains with the bullet after it leaves the barrel.

Yes velocity and RPS (rotations per second) slows as the bullet travels and this too can be calculated. Quoting RPM is just a standardised convention, whether you call something 12,000 RPS or 180,000 RPM the speed of rotation is EXACTLY the same.

Hope this helps clear this up for you.

 

[coloradoclyde]

You sure like to make assumptions :shake: ....

 

[Artificer]

As has been noted, perhaps a few times to many, I'm new to this forum, but I hope it's not one of those forums where one gains ascendancy through simply posting a lot. If that is the unfortunate case, I'm afraid I'm way behind you guys with several hundred posts.

Gene,

Though we are human and all make mistakes here as in any other endeavor, posting a lot does not cause one to gain ascendancy on this forum.

On this forum, we are free to disagree (even most passionately) as long as we do not make personal attacks on others.

What does cause one to gain ascendancy here is how we reply/act towards others and the information we bring to the forum. There are many forum members who do not post nearly as much as others, but are still thought of highly.

Gus

 

[Artificer]

The example you gave with the football illustrates why a faster twist stabilizes a bullet better. The velocity may be greater, but so is the twist applied to it. So the QB is shooting from a fast-twist arm.

Have to admit I do not follow your reasoning on this. There is only so much twist or spin the hand can put on a football, no matter how much force is used to throw a ball.

But what the football example does show is when more force is applied to the football, it will spin faster and go farther after it leaves the Player's hand than it did with a softer throw. This mimics the external ballistics in a rifle.

Gus

And only so much spin you can put on a bullet. Limited by the twist of the barrel. The range of possibilities on either a football or a bullet are limited. They are not infinite.

Sure, I agree with this paragraph and there is a finite amount of spin you can put on a football in the human hand. Thus throwing it harder from the same human hand increases the distance it travels and how fast it spins after it leaves your hand.

Gus

 

[Gene L]

I think I begin to see something here.

Of course the examples you gave are correct, and I don't argue that it takes a certain velocity in your given example to reach stability.

However, I've shot .36 caliber bullets with 50 grains of FFFG, and got OK stability and pretty good accuracy. It was blowing powder out the barrel. So I dropped that down to 20 grains and still got good accuracy. I'm not clear exactly how strongly velocity applies to round ball accuracy. The range of tolerance seems to be pretty great with a round ball and a (estimated) 50 twist. I've heard of those who shoot even less powder, although I've never tried it myself. What I suspect from my personal experience is that while velocity changed in my rifle, the RPM (or RPS) of the ball remained relatively the same. And I infer from that is it is probably true with other MLs shooting round balls.

I don't remember what the twist is on my rifle, am guessing 50, I assume it's slow. But I do know with my experience and from what I read with others, you can vary the velocity and get fine accuracy. If there's a limit where a round ball becomes unstable, I haven't reached it yet and think it falls outside practical experience.

If this is a false experience, let me know. Shoots fine.

 

[coloradoclyde]

And only so much spin you can put on a bullet.

Yes and I noted that early on...

Yep!, more powder = more velocity = more stabilization = better accuracy....But only to a point.

 

[Artificer]

Great explanation, Dean. :thumbsup: :hatsoff:

Gus

 

[coloradoclyde]

Gene,
It might help you understand better if you learned how a propeller works. Or better yet a variable pitch propeller and its relationship between the air passing over it and the velocity of the plane and propeller.

The pith of the propeller is analogous to the rifling in a gun and the air moving over the propeller is = to velocity.
As the relation ship between the two changes the rotation speed (RPM) of the propeller changes.....

Any of this starting to sound familiar? :hmm:

 

[Artificer]

Gene,

OK, now I see better where you are coming from, I think. :wink:

I thought about bringing this up before, but did not want to sidetrack the discussion if you had not seen it before.

What I learned back in the 70's was there were TWO powder charges that gave the best accuracy in a rifle and that includes black powder or modern rifles as well.

For example, my "Target Load" in a .45 Cal. 1/48 twist barrel was 42 1/2 grains of FFFG black powder. This shot extremely tight groups at 25 and 50 yards. However, there was not enough "oomph" or power in that load for taking mid to large size game. So I began increasing the powder charge.

As I increased the powder charge for a hunting load, at first accuracy went to Heck in a Hand Basket. It wasn't until I got up to about 80 grains where the accuracy came back to about the same as the target load. When I increased beyond 80 grains, accuracy began to fall off as well.

OK, so what the Heck caused these things? The light target load was just enough that it stabilized the bullet well at a lower velocity. However, to stabilize the ball at a higher velocity, it had to have more powder up to a point. After the Hunting Load went over 80 grains of FFFg in that barrel, accuracy once again declined.

I really think this term is way overused nowadays, but what I found was the two "sweet spots" were the ball stabilized best at different velocities.

BTW, I had an original .36 cal. circa 1850 percussion rifle that was THE most forgiving rifle I have ever known, as to the powder charge and ball size WHEN only shooting targets at 25 to 50 yards. It shot as well as most any human could do with a fairly wide spread of powder and even to some degree ball/patch sizes. I'm sure that rifle would have shown more differences in accuracy with different powder/ball/patches had I shot it at 75 yards or longer distances, but I just never shot it that far.

Gus

 

[Gene L]

To go off-topic even more in my effort to convince everyone I'm not insane, consider this. My 223 puts a factory load out there at 3200 fps. It shoots about 1/2 MOA.

However, I can drop that velocity down by 1000 fps and in the same rifle and it still will shoot pretty well. Nothing like MOA, but the bullet is still stabilized. That's a reduction of 33 %, roughly.

I think it's a 10-twist. I don't know how low it could go and still stabilize the bullet and don't want to learn. No practical reason.

A .32 round ball is about 45 grains, (IIRC) like a .22 LR and the bullet will stabilize at a quite low velocity. Very low, in fact. It can lob bullets at 40 yards and still hit the target. When I dropped down to 20 gr. in my .36, the accuracy improved...not by much, but enough to convince me to stay with that load.

Every rifle I've ever owned, both BP and Smokeless has a sweet spot.