Rate of Twist?

[hanshi]

I would believe it may have more to do with the minor variations between barrels than rifling. It would seem, however, that twists either fast or slow in the extreme would definitely tell a different story.

 

[William O.]

I'm saying that the bullet might start wobble a bit at longer yardarge but it's not going to tumble end over end. Even a slower rate of twist is going to impart some spin on a conical bullet and I am referring strictly to muzzle loading and not to any extremes.

 

[illuveatar]

I don't have any firsthand knowledge when it comes to bullets tumbling since I only shoot roundballs and they don't leave keyholes. So I'm not going to argue the point, I'll let this post from Zonie do the talking instead.

With an elongated bullet a fast spin is needed to create a gyroscopic effect to keep the bullet from tumbling, or turning end over end and leaving a "keyhole" shape on whatever it hits.

With a roundball the spinning from the rifling is not needed to keep the ball from tumbling but it plays an important part in keeping the ball flying in a true direction.

The surface of a roundball is not smooth and uniformly shaped although it does look pretty good to the human eye.

To the wind at subsonic and supersonic speeds it looks much different. The uneven surface will develop different pressures from the air blast and if the ball is not spinning (like it was fired from a smoothbored gun) these unequal pressures will cause the ball to be pushed off course. The direction it will fly is impossible to figure out.

If the ball is spinning about the axis of its flight these same pressures are trying to deflect the ball however because it is spinning the actual direction of deflection is always changing.

Put another way, lets say that at one position the pressure is pushing the ball to the right.
If the ball was not spinning it would start going to the right immediately after leaving the muzzle.
With it spinning, just about the time the pressure was going to push the ball to the right, it is now trying to push it downward to the right, then down, then down to the left, then to the left, then up to the left, then up, and so forth.
The deflecting pressure is always changing its direction about the axis of the balls spin and along the axis of its flight. The net effect of all of this is the ball is not really deflected at all so it continues to travel along its trajectory towards the target.

To accomplish this great task the ball does not need a super fast spin so the slower rate of twist works fine.

The slower rate of twist does another good thing for a patched ball. It does not tear up the soft cloth patch even if some very high velocities are used.
This makes a slow twist barrel much less sensitive to high or low powder loads (velocities).

This provides good insight into the the aerodynamics of flying lead IMHO. :v

 

[Loyalist Dave]

actually, it's a function of the diameter of the projectile vs it's length, coupled with acceleration rate plus the twist rate of the rifling, that determine if the bullet of any design with stabilize or skip across the rifling in a rifled barrel.

See The Sporting Rifle and Its Projectiles by James Forsythe c. 1867 for details.

I have a .45 rifle with a 1:60 twist that will not stabilize a conical bullet, but a .58 3-Band Enflield with a 1:72 will do so quite well.

LD

 

[nkbj]

48" twist in a .58 is plumwunnerful. Works for round ball and long ball. Surely there must be such a twist for every bore diameter.

 

[Sperit de bois]

Here to refered to as Cross Sectional Density (ratio of lenght to width)
And the result called Ballistics Coafficient,,,,Fat and short doesnt stabalize to well ,,in some cases,,,but long and skinny now that is stable,to a point. And you can push a projectile fast enough to become unstable(tumble)and make it slow enough(wobble) to do the same.
Every weapon I own has it's own sweet spot,eats some loads no problem others it just doesnt. Not a bad thing,,means I have to shoot more.

 

[Zonie]

My comments quoted above were mainly speaking of patched round balls.

As for spinning elongated objects, it's a different world.

At certain rotational speeds all shafts are out of balance and of course this includes shaft like projectiles like bullets.

Basically, the longer the shaft (or bullet) is when compared with its diameter, the lower the speeds needed to cause the imbalance to occur.
The rotational speed where the imbalance is worst is called the "critical speed". With all shafts, there are several different "critical speeds".

An example of length vs speed in spinning shafts is the drive line in a car.
If it is small enough in diameter and long enough it will start shaking so much as it tries to start turning end over end that the whole car is effected. That is why some long based vehicles like trucks have two drive shafts with a center bearing supported by the frame in the middle.
The two shorter shafts are operating below their "critical speed".

The interesting thing about "critical speed" is below that speed everything runs smoothly.
Also, above that critical speed everything runs smoothly until the next critical speed is reached.

Getting back to bullets, they also have critical speeds based on their length to diameter ratio.
Long skinny bullets are quite unstable because their first critical speed is quite low.
Short fat bullets are quite stable because their first critical speed is so low the rotational velocity can be easily be achieved getting them above the first critical.

Bullets also have high velocity wind to contend with.

When a bullet in flight starts to wobble due to it being around its first or second critical speed, the wind instantly deflects the nose causing the bullet to tumble end over end.
Where it is at in its tumbling is a matter of distance and if the target is at the right distance you will see where the bullet was going sideways as it passed thru the paper.

Years ago the Greenhill Formula was devised to calculate the rate of twist needed to spin a elongated projectile at a speed between its critical speeds so that it would stay 'stable' as it flew towards the target.
It uses the projectiles diameter and its length to establish a ratio and usually assumes a standard velocity to calculate the minimum rate of twist.

While some feel there are better formulas to deal with this issue (and I'm sure there are), in general the Greenhill Formula works quite well for us black powder shooters.

 

[Dr5x]

I must ask deer hunters on this one.
An old Colorado Hunting guide wrote me that he was thrilled when the Maxi Ball first showed up.
In hunting he found that while both the Round ball and the Maxi ball would kill a deer, the round ball tended to exhaust all its energy in the deer while the Maxi ball would go through and through and expend a lot of its energy down range beyond the deer.

The effect of this, he told me, was that the round ball is more likely to drop the deer in its tracks while elongated Maxis ball would result in the deer running a good distance before finally dropping..

I have no experience on this subject but feel the deer hunters could give me their opinion,

Dutch

 

[David W.]

Here to refered to as Cross Sectional Density (ratio of lenght to width)
And the result called Ballistics Coafficient,,,,Fat and short doesnt stabalize to well ,,in some cases,,,but long and skinny now that is stable,to a point. And you can push a projectile fast enough to become unstable(tumble)and make it slow enough(wobble) to do the same.
Every weapon I own has it's own sweet spot,eats some loads no problem others it just doesnt. Not a bad thing,,means I have to shoot more.

You don't need to take into account, a conical going too fast out of a ML to cause tumbling. Tumbling usually is related to a projectile rotating too slow vs. too fast in relation to the length/diameter ratio.

Fat and short, such as in a round ball doesn't mean inaccuracy.

There are three factors that influence penetration.

1. Initial velocity
2. bullet weight
3. Distance

 

[Rifleman1776]

Absolutely correct.
But, very many shooters, ml and modern, have a mindset that a bullet must pass through completely to be effective. A form of 'magnumitis' I suppose. They like the blood trail finding a shot animal. Personally, I prefer to drop them where they stand to avoid tracking.
Logic will not prevail in a discussion like this. The 'more is better' crowd cannot be swayed.

 

[Rifleman1776]

Fat and short, such as in a round ball doesn't mean inaccuracy.

There are three factors that influence penetration.

1. Initial velocity
2. bullet weight
3. Distance

Pretty much all wrong and misleading.
Round ball does not mean accuracy or lack of it. Proper loads and loading determine accuracy.
Many other factors enter into the penetration equation.
e.g. size of animal, it's fur, etc.
Of course bullet/ball size, composition, velocity add to the computation.
Regardless, enuf is enuf. There is no such thing as super-enuf.

 

[roundball]

I must ask deer hunters on this one.
An old Colorado Hunting guide wrote me that he was thrilled when the Maxi Ball first showed up.
In hunting he found that while both the Round ball and the Maxi ball would kill a deer, the round ball tended to exhaust all its energy in the deer while the Maxi ball would go through and through and expend a lot of its energy down range beyond the deer.
The effect of this, he told me, was that the round ball is more likely to drop the deer in its tracks while elongated Maxis ball would result in the deer running a good distance before finally dropping.
I have no experience on this subject but feel the deer hunters could give me their opinion,
Dutch

A couple of things:
1) from the nature of all you quoted him as saying, his logic on PRBs vs. conicals, I don't understand why he would be thrilled...LOL...seems counter to his beliefs.

2) With all due respect to the individual you quoted, based on my own experience and logic with both PRBs and conicals, his claim shows a real lack of understanding and frankly an old wives tale that keeps getting repeated as gospel by those who simply don't know first hand.

The only valid claim that can be made about a projectile that stopped somewhere inside an animal is that indeed, it stopped because it used up all the little bit of energy it had and stopped inside...it ran out of steam...couldn't make it through...resulting in a reduced effect on an animal, etc.

It made the initial hit and immediately began slowing down, stopping somewhere...25% of the way in...50% of the way...75%...creating a wound channel only 25% of the way through...only 50% of the way through, etc...AND...factor in longer and loner distances, the inadequate penetration & reduced wound channel becomes exponentially worse...so you see the fallacies right away.

Conversely, a larger heavier projectile...doesn't even have to be a conical...driven with enough power to pass completely through the vitals of a head of game, means that it created an ever increasingly larger wound channel the full width of the internals...it created maximum internal damage and disruption to more vitals...it cut more blood vessels with its longer / larger would channel, etc.

AND, the more power applied to a projectile, the greater distance at which it will give max or near max penetration and performance. A light load that stops halfway through an animal at 40-50yds will barely make it in at 100yds.
Personally, I'm always disappointed if I DON'T get a complete pass-through and try to troubleshoot the reason why to correct it next time if a correction is needed.

Muzzleloader hunting with sidelocks is basically just an extended form of Bowhunting.
Hemorrhaging, not hydrostatic shock, is the mechanism...MLs simply do it at longer distances that the typical arrow/broadhead.
The longer / larger wound channel you have, the better off you always are...ask any bowhunter if he'd rather have his broadhead stop 3-4" inside an animal or have those razor blades pass completely through the full body width of vital organs and blood vessels.

I suspect your own instincts and logic were what led you to post the question.

 

[Dr5x]

The old guide added that when the deer runs rather than drops, it runs in a direction that seems to always be away from the hunter's vehicle.

Dutch

 

[Dr5x]

Thank you, Roundball.
What you write seems quite logical. I assume other hunters agree.

The guide's "thrill" was before he learned that in his opinion the round ball was superior.

Dutch

 

[Rifleman1776]

The old guide added that when the deer runs rather than drops, it runs in a direction that seems to always be away from the hunter's vehicle.

Dutch

Fer certain, fer sure. And, in the Ozarks that direction is always downhill. :shocked2:

 

[Dphar]

According to people I know and people on the WWW who have discussed them the Maxi-Ball is a dismal hunting projectile. Probably why the Maxi-hunter was invented.
A 440 gr ball is far more effective than a 440 gr Maxi Ball at hunting ranges.

The maxi design allows the front band to fold into the front driving band, when this occurs and its apparently common, the bullet does not expand and makes a very poor wound channel according to reports. I was shooting a RB and was a traditional sort of guy when this thing was invented so I have only shot about 10 of them. It will penetrate about double what a RB will to 150 yards in baffle board tests I did 30 odd years ago (at the insistence of my editor). But a 54 RB will penetrate well enough to kill Canadian Moose at 175 so what it gained? A friend saw it done and came down off the hill and lasered the distance. One shot kill Moose did not make 30 yards IIRC. Everyone but the shooter thought it was ill advised at that distance. But the ball DID penetrate to the off side hide.

The Maxi was invented to:
1. Sell to people.
Who;
2. Did not care to learn how to use a PRB
3. Believed what the poorly informed gun writers were writing to aid in #1. That the round ball was too old fashioned and low energy to kill anything.
(Besides TC was buying advertising and MUST be kept happy).
But its faults and shortcomings were somehow left out, assuming the writer had enough experience to even realize there were any.
This drivel continues to this day.
Now its plastic Sabots, copper bullets and 777 fired with a shotgun primer.

Dan

 

[asbrown]

There's a simple solution to the rate of twist question. Theres a formula devised by ballisticians in the 1800's that still holds true today for everything from round ball to the longest ogive styled bullet made.
Bullet length divided by caliber gives length in calibers.
150 divided by length in calibres X calibre =twist

a .50 RB is .5 long
divided by .5(calibre) = 1
150 divided by 1(length in cal)X .5(cal)= 75
minimum twist to stabilize a .50 RB is 1/75

For RB its easier to just multiply the calibre times 150. A .40 twist is 1/60 a .32 is 1/48 and so on. This is just a minimum twist necessary to stabilize the projectile. A faster twist can be used but powder charges may need to be lowered for best accuracy.

 

[Dr5x]

There is a common assumption that the old folks did what they did because they didn't know any better.
I think I was guilty of that when I first began shooting ML rifles and felt that my 3- 4" groups were about as much as one could expect from the old timers systems.

The some spoil sport showed up with a flintlock and consistently got 1 inch groups at 50 yards shooting an odd offhand style with his left arm supporting the rifle while hie left elbow was pressed against his chest. He was steady as a rock.

Dutch

 

[Dr5x]

Back in the '70's when I got into Black Powder I was told that the 1 in 48 twist was a compromise twist that would handle both Round Ball and Elongated bullets.

With faster twists it is considered wise to back off a bit on the powder charge because the higher charge will rip the belt of the round ball off completely thus destroyer any hope of accuracy..

Dutch

 

[nkbj]

This afternoon I'm lapping and trying out a 1:48" twist .58 barrel on a TC Hawken. Checking out a RCBS 500 grain minie mold that has the rings enlarged to allow sizing the back half of the minie down to .580" and have the front engrave on the rifling. Looking good.

Does anybody know what the rear diameter is on a .58 REAL?