Why is a fast twist bad for a round ball?

https://www.vcalc.com/wiki/AndrewBudd/Greenhill+Formula+for+Optimal+Rifling+Twist+RateGreenhill formula for stabilizing a projectile. Uses velocity, mass,diameter and length.
All of the answers are correct in one aspect or another, but longer projectiles require more twist to maximize accuracy.

Don

Have a read of 'The Sporting Rifle: And Its Projectiles (1867)' by James Forsyth. He approaches it from the direction of why a slow twist s good for a round ball. The Sporting Rifle and Its Projectiles : James Forsyth : Free Download, Borrow, and Streaming : Internet Archive is a free download or read.

A 1-48" twist is not necessarily bad for round ball. I've owned several very accurate .50s that shot great with that very ROT. My .32 & .36 have a 1-48" and shoot one hole groups.

More important than the rot is the depth of the rifling. A barrel with very shallow grooves "can" allow the prb to strip over the grooves rather than get a good bite. This is why some rifles with 1-48" are difficult to work up an accurate prb load for. Note that 200 + & - years ago 1-48" was a common twist in rifle barrels. European jaegers sometimes had twists as fast as 1-24". If your barrel has those very shallow grooves you may need to experiment with a larger ball or a thicker patch. In any event a good shooting load is more than merely "possible.

with a round ball the faster the twist the shorter the trajectory.
also the larger the ball the slower the twist needs to be.

Drop a torn piece of paper from directly over a given point on the floor. you could even use a small trash can as "target". Part of the time the random movement of the paper will make it not go in the can. Then try spinning the paper as you release it. If you spin it right it will go in the can more often.
Same for round ball.

Because of not being for stability, fast twist is bad for inappropriate rifling geometry rather than bad for the spherical projectile.

You can actually shoot RBs in a fast twist but you have a narrower load parameters. I have a 1/20 54 that will shoot RBs accurate but I have only shot light loads in it.

TANSTAAFL said:

I have read a couple of theories on the issue. One is a heavy charge can cause the RB, with it's minimum rifling contact, to jump or strip the rifling, another was the fast twist with heavy charges will over stabilize the RB.

With light target loads, the faster 1:48 twist rifles are normally very accurate indeed.

Many English originals utilized a faster twist with their RB muzzleloaders, they did not charge them as heavy as American makers of the era.

Below excerpted from:[url] http://blackpowderonline.com/JAN02ENGLSHRFLS.htm[/url]

Twists in these English rifles varied. Some had fairly rapid twists which gave little latitude in the effective powder charge. Fast twist rifling may cause erratic accuracy if very heavy charges were used. Slow twists were also used. Slow twists in large bore muzzle loading rifles are more forgiving, if the shooter desires to use a heavier charge.

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Your absolutely correct about English & European rifles having a faster rate of twist & most also have much deeper rifling. After 50 plus years of shooting I've stuck with using these fine old originals in competition & for hunting as they are capable of shooting far tighter groups than I am capable of when properly loaded with a lubed patch that fills the rifling when compressed with the right diameter round ball. With 80 grain charges it maintained consistent accuracy through a full day of competition without cleaning.
This .70 cal. Danish built Jeager by I.C. Haugaard in Kiobenhaven has been my favorite hunting & competition rifle for over 40 years & can honestly say is the most consistently accurate rifle I have ever owned.

Twist good or twist bad? It's more about the whole barrel and twist rate is one part of it. Consideration has to be given to the depth of grooves, then its the width of the lands, the ratio of the land width to the groove width, and to a lesser extent are the grooves square cut or radiused grooved. As stated above some original round ball rifles were built with fast twist rifling. Short barreled jaeger rifles were designed around having a full twist in the length of the barrel. These were short barreled rifles of 28" and sometimes less length with a full turn twist. These rifles were capable of excellent accuracy.

You can't determine good or bad until you have groups on paper.

My musketoon has shallow rifling 1-48 twist, and will shoot a 500 gr minie into under 3 MOA at 100 yards. But try and get a prb to stay on a pie plate at 50 is a struggle unless you drop the load to 30grains fffg. So I am certain a shallow rifling will let a prb strip the rifling unless you lower the velocity greatly. My friend's 54 TC Hawken has a deep groove 1-48 twist, it shoots nice clover leafs with anything from 50-90 grs ffg at 50yards with prb's.

Someone please have the Mods rename this post Lazarus!!

Just get the new Lyman mould designed for fast twist. P/N .50FTRB Mould. Designed for the guy with fast twist in mind. Box says its not different, they just say it is.

Normally most everything is correct, but that is only normally speaking when talking ML'ers. I purchased one of the last barrels the old Green River Barrel Company made. It was a 45 Caliber barrel with 1 in 60" twist. Knowing you couldn't hunt deer in Utah with a 45 caliber round ball and knowing my wife couldn't hold up one of the heavy hawkens we went to the 7lb. GR Barreled gun. We shot several different elongated bullets that wouldn't hit a sheet of plywood at 100 yards and then we found a very long bullet that was a tack driver shot after shot.
The next story comes when Green Mountain Barrel Company made a 32" X 1" X 28" twist, with deep groves, for a short while. I made a 50 caliber Hawkens with one of those barrels. It was a tack driver with real black powder, and a elongated bullet, but with the Pyrodex, Triple Seven, etc the groups were terrible. I tried and tried to get a better group, nearly broke the bank to find a substitute powder, but never did. To this day when you shoot REAL black powder it is a very accurate gun.
Muzzle-loader shooting can be as good as it comes or just drive you nuts on some specific guns.

RAEDWALD said:

Have a read of 'The Sporting Rifle: And Its Projectiles (1867)' by James Forsyth. He approaches it from the direction of why a slow twist s good for a round ball. The Sporting Rifle and Its Projectiles : James Forsyth : Free Download, Borrow, and Streaming : Internet Archive is a free download or read.

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I am sure one used to be able to edit one's posts but apparently not now. That reference should be: The Sporting Rifle and Its Projectiles : James Forsyth : Free Download, Borrow, and Streaming : Internet Archive

It seems logical that given X amount of energy from the powder charge, if more/faster rotation is imparted to the projectile, thus creating rotational momentum, then less energy is available to produce linear muzzle velocity.

Eterry said:

My musketoon has shallow rifling 1-48 twist, and will shoot a 500 gr minie into under 3 MOA at 100 yards. But try and get a prb to stay on a pie plate at 50 is a struggle unless you drop the load to 30grains fffg. So I am certain a shallow rifling will let a prb strip the rifling unless you lower the velocity greatly. My friend's 54 TC Hawken has a deep groove 1-48 twist, it shoots nice clover leafs with anything from 50-90 grs ffg at 50yards with prb's.

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Once tried round ball in a .69 caliber Fremont. Turned out that hard ball shot better because those wide lands acted like a smoothbore!

hung load said:

My Traditions Deerhunter .54 cal, sidelock, percussion has a 1:48" twist.

I've read that slower twists are preferable for balls and faster for conical bullets.

1:48 seems pretty aggressive (barrel length is around 24"). How does this affect accuracy of a ball exactly?

Here is my close copy of Jim Bridger's Hawken. This is an Oregon Barrel Company custom barrel with a 1 in 48" twist, like Bridger's. The target on the left was shot with the sun on the sights, but I shaded the sights for the right-hand target. I'd filed the front sight down to raise the group. Don't know why the velocity difference, both with 50 grains of Goex 3F.

The second set is with 100 grains of Olde Eynsford 1 1/2F, weight corrected measures for all.

Third target is with 120 grains of OE 1 1/2F in that 1 in 48 inch twist. 1924 fps, 50 yards.

Bottom photo is my .54 Kit Carson inspired deer rifle, with a Hopkins and Hobbs 7/8" barrel in a one in 48" twist. Velocities about 1565 fps.

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Hung Load hasn't been here since 2006, so he can't thank those of you who responded to his request for help. But I appreciate your replies and learned from them. So here is my deer rifle.

I think there is more to picking the "ideal" RB twist than just caliber. The formula says usually about 1.3x-1.4x caliber, but there is something to be said for the rotational speed of the surface too. A 4 bore might have a 1:125 twist and a 50 cal 1:66. Other posts have said the "magic number" on rps's is around 300-400. Other posts have said with a pistol, you need at least 1/4 turn in rotation to stabilize a bullet / ball.

At that twist, a 4 bore (1.00") would need to be zipping along at 3125 fps to attain a 300 rps rotational speed to have a stabilized ball. I don't even think that's a possible mv out of a BP gun

I am confused, so if a ballistician can weigh in here I would be grateful.

hung load said:

My Traditions Deerhunter .54 cal, sidelock, percussion has a 1:48" twist.

I've read that slower twists are preferable for balls and faster for conical bullets.

1:48 seems pretty aggressive (barrel length is around 24"). How does this affect accuracy of a ball exactly?

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When I started shooting black powder 60 years ago I knew very little about what I was doing but fortunately a local antique arms collector helped educate me. I did know that I wanted a rifle & pistol that was accurate so he took me shooting with a nice original English percussion sporting rifle & an English flintlock pistol. Both had fast twist rifling & accuracy was excellent & shot very tight groups.
He explained & demonstrated how the accuracy was consistently excellent because they had faster-twist rifling than what we see used in most of today's firearms & the rifling was also much deeper. The groups remained equally tight with light, medium & heavy charges accuracy, only thing that changed was elevation of the groups. The trick to maintain accuracy was using the proper thickness lubed patches, they prevented the balls from skidding.
Now at 78 I'm still shooting mostly vintage firearms from .40 to .70 cal. & the ones I've built have custom barrels with similar bore specs.
Just my opinion but I think most of today's commercially built muzzle loaders have shallow rifling with longer rates of twist because they are more forgiving. Over the years I've noticed at bigger shoots like Friendship that most of the serious competitors are shooting custom built firearms or originals.
What is needed now is a magic group-tightening formula for us shaky old farts.