Rifling Twist in Relation to Bore Size

[Reegee/Flint]

Is there a formula for rifling twist in relation to bore size? Bigger bore less twist?
Curious to know.

[Frank]

Per John Baird who was probably the quintessential expert on Hawken rifles. Every Hawken was a 1 in 48 twist regardless of caliber. I think Jacob and Sam knew what they were doing. There were several articles in the Buckskin Report on shooting original Hawkens. They were extremely accurate.

[R Whittington]

Ned Roberts book deals with, buy mainly bullet guns. I’ve found that almost any twist can be made to shoot round ball. Just my experience.

[Bob Roller]

My Henry barreled Whitworth* with 40-45 grains of 3fg shot well at 50 yards.I used this load with a patched round ball so small boys could fire it without having it kick them off the rest.According to original powder measures the loads were moderate and the practice of using over 100 grains was not used.A 1 in 48 twist will work.One of the original Hawken rifles with original measure showed about 55 grains and that could be doubled for a longer shot or a harder hitting up close shot.The late Don Brown rold me of very high velocities with heavy charges in his Henry copies with very slow twists that sounded more like splines than a rifling twist.*The Whitworth was a 1 in 18 and made for a bullet of more than 500 grains in .451.
Bob Roller

[Daryl]

Is there a formula for rifling twist in relation to bore size? Bigger bore less twist?
Curious to know.

No formula that I know of as this is an inexact science. So much depends on the ball's fit in the grooves.

If you google GM muzzleloading barrel rate of twist, or look them up on Track's site, along with the other barrel makers, you will find out what that makers of today use.
Suffice to say, up to 40gr. calibre 48" ROTwist is quite normal.  .45 cal. 48 to 60" ROT, .50 cal 60 to 72", .54 cal. 60" to 80".  The .58's of the Civil War used 48" to 78" ROT's
and those shot mostly Minnie Balls (short conicals).

My .69 has a 66" ROT and shoots accurately at 50 yards with 82gr. 3F or 85gr. 2F. Longer ranges, it shoot accurately from 125gr. 2F up to 200gr. 2F.
Taylor has a 16 bore Lang rifle built in1853 that has a 48" ROT and it shoots very well indeed, with 85gr. 2F, to 100 meters.
Generally speaking it takes very little spin to stabilize a round ball.
Generally speaking, the larger the bore, the slower the twist required. Same goes for modern guns.
Generally speaking, the lower the velocity, the faster the twist has to be.
Generally speaking, the faster twists will not admit as much powder (velocity) as the slower twists.
Generally speaking, the slower the ROT, the more powder is needed to get good (the best) accuracy.
Generally speaking, the slower the ROT, after a given point, the looser the combination can be and still get decent hunting accuracy. This is where the very slow, shallow Forsyth-type rifling comes in. Forsyth spoke of rifling twists of 1/4 turn in the length of the common SxS rifle's of the day, which was 26", thus 102" ROT. He also spoke of 8foot (96") and 12 foot (144") ROT's.
He was concerned mostly with shooting large and dangerous game in India, but deer as well.
Generally speaking, the slower the twist (as per Forsyth), the shallower the rifling CAN be as less stress is put on the "fit" of the round ball and patch to keep pace with the ROT & not strip, or as he said "trip over the rifle".

[RichG]

https://www.ctmuzzleloaders.com/ctml_experiments/rbballistics/rbballistics.html
this might help
as stated the larger the ball the slower the twist and the smaller the ball the faster the twist. I think it has a lot to do with the mass of the ball.

[Mike Brooks]

1 in 48 is perfect for all calibers. Westerners may disagree as they tend to shoot longer distance for hunting

.

[Reegee/Flint]

 :)Lots of good info.........Thanks

[Bob Roller]

What IS long range for a round ball rifle? I saw a video of Mark Brier's two youngsters shooting a flintlock long rifle at 200 yards and they were ringing the gong.How much velocity is lost from muzzle to target at 200 yards? Has anyone  REALLY done anything beyond speculation on this?I would think velocity would be shed fairly fast because of the shape of the projectile and the low pressure propellants used.
Bob Roller

[Frank]

I am sure there was plenty of long range hunting back when the Hawken brothers were making rifles. Plenty of elk and buffalo back then and the Hawken rifle was very effective.

All of today’s barrel makers and shooters were raised with modern ballistic tables, foot pounds of energy, velocity, etc… This stuff applies to modern cartridge rifles. Black powder, lead round balls, and muzzleloaders are a totally different animal and modern ballistic tables do not apply.

When it comes to barrels and muzzleloading rifles, my money is on the Hawken brothers and their 1 in 48 twist barrels. No disrespect to those of you who think otherwise.

[Bob Roller]

I once read that it was Joseph Whitworth that made it a bad idea to be exposed at 1000 yards and this was pre 1860.
Ballistics are what they are and that's a fact,Recently I saw a posting about hitting a gong at 500 yards with a round ball.
I would like to see how much the disfiguring of that ball was and I am assuming soft lead and what caliber.
Here is something to think about.Tom Dawson had the Parkman Hawken,a J&S marked Hoffman and Campbell with a 42 inch
50 caliber barrel.He made a very good copy with an identical barrel made by Bill Large.In a test,the antique would show higher
penetration than the new barrel of same twist and caliber and the round balls came from the same mould with identical weights
and powder charges.Parkman's diary claimed a buffalo was killed at a good distance and I forget what it was.I gave my copy of
that to Bob Woodfill and it was a hardback book from 1905.I am thinking Parkman had a better quality of black powder then because
that was the only thing around back then.What he had may have been like Swiss today.
Bob Roller

[Frank]

To add one more thing. All of the Hawken rifles had slightly coned muzzles.

[Bob Roller]

The coned muzzles would aid in loading.Maybe you are thinking of a tape or constriction sometimes called a choke.
Bob Roller

[Frank]

The coned muzzles would aid in loading.Maybe you are thinking of a tape or constriction sometimes called a choke.
Bob Roller

Nope not at all. I added the coned muzzle fact to show it was a common practice and it was done to increase ease of loading

[Fyrstyk]

Check out CTMuzzleloaders.com for round ball ballistics tables.  Eye opening.

[WadePatton]

It varies because stabilization has to do with RPM/mass/shape and the RPM varies by velocity.

I used to study this stuff deeply.  Then one day I realized that most all the successful black powder barrel makers have worked it out pretty well. It's in their best interest to get you the most accurate barrel for your purpose. Also there's no magical nothing to rediscover in projectile stabilization via rifling. I now trust the small shop makers to put in whatever twist they like (for my purposes) and I'll shoot it.

Good luck with your endeavor for the perfect Rate of Twist, but know that there are tradeoffs in this, as in most everything.

[Daryl]

Target shooters usually use the best- best barrel makers, IE: those who make the most accurate barrels.

So - need to talk to the round ball Bench Rest shooters, or cross stick match winners, the plank and chunk winners - what barrels do you use?
What caliber and what ROTwist are they. How much powder.

I know of a plank winner uses a .50, cal gain twist barrel with 110gr. Swiss for their matches which take place at 60yards.  I suggest that a
.50, no matter what the twist rate, loaded with 50gr. of 3F would not be competitive - in the least, even if it was a tight load.

I do happen to know that some Round ball BR shooters favour the .69 calibre and HUGE powder charges, not meant for 8 to 10 pound rifles.
They use what works and shoot at 100 and 200yards, I think.

I recall reading about NMLRA cross stick matches back in the 70's, the most favoured was .50 cal. and most favoured rifling twist was 48".
When the range increased to 100 and further, the calibre and powder charges increased drastically, seems to me.

Too - there are no winners in these matches, thumb starting the ball.

[yulzari]

The rate of twist is prortionsl to the rotational momentum of a round ball.As the bore increases not only does the mass massively increase but so does it’s distance from the centre which multiplies the rotational momentum.

Thus we see small bores needing a fast twist to stabilise the ball whereas the larger heavier larger bore rifles can gain the same stability with a slower rotation. Now as to the mathematics of the relationship I am not fit to advise but the principle is clear.

In addition the slower the twist the less it is sensitive to velocity so one can adjust the sights (or rather not adjust the sights) by adjusting the charge to compensate for the distance. This assumes that the actual twist is sufficient to stabilise the ball. But spherical balls need little spin but then we feed back to the rotational momentum being proportional to diameter as above.

More empirically, a .32 Crockett I has good accuracy with a round ball at a 1:48” twist and a .58” ACW rifle musket is accurate with a round ball at a 1:78” twist which gives one a guide. FWIW the rifle musket figure conforms to Forsyth’s system as it happens.

[Daryl]

I got decent accuracy with a 72" ROT Zouave with thick patch and .575" RB at 100 yards, but it took 120gr. 2F GOEX, back in 1977 or 78. Unlike the actual 'rifled muskets that had progressive depth rifling, the commercial "Remington" Zouaves of the day, had .003" depth of grooves. By decent, I am talking 5 shot groups of 2".
My 66" twist Bill Large barreled Hawken, required 140gr. of the same powder, to achieve it's best at that range - 1 1/2". Still kicking myself for selling that rifle.
According to my notes, 140gr. 2F produced 1,683fps av. with spit for lube and 1,736fps with bear grease for lube.
With spit the Vel. variation on 10 shots was 10fps, but with Bear Grease, it was 69fps.
160gr. 2F, also accurate, produced 1,810fps and 8fps variation with spit, but 1,867fps with the Grease and 74fps variation.
While slower twist rates usually demand more powder, this isn't concrete, as in the case noted, the faster twist needed 20gr. more powder than the slower twist barrel.
Individual barrel characteristics come into the equation when dealing with accuracy. Mind you, the Zouave had a relatively thin round barrel, while the Hawken had a 1 1/8" octagonal
barrel.
Both of these guns could barely keep 5 balls inside 12" at 100yards, with a mere 95gr. 2F powder. My notes show that powder charge produced 1,424fps spit lube and 48fps variation.



numbers remove duplicates

[D. Taylor Sapergia]

I don't think there is a relationship for bore size to rifling twist.  As an example, my original Lang rifle in .66 cal has a twist of 1:48", as do all three of my .40 cal rifles.

[rick/pa]

At one time I ran across a formula for calculating the most accurate load using ball weight, ball diameter, and rifling twist. It's not the  Greenhill or Davenport formulas and it was only for round balls. I tried it against several of my rifles using different calibers and twist rates and found that my most accurate loads that  I found by experimenting were within a grain or two of the calculated loads. Has any one ever seen a similar formula? I lost it when the computer I had it on crashed.

[Jeff Murray]

Interesting thread.  Bob commented on velocity at 200 yards.  According to Lyman's Black Powder Handbook circa 1975, a 50 caliber round ball starting with a muzzle velocity of 1800 fps would be flying at 1033 fps at 100 yards, 754 fps at 200 yards and a melo 584 fps at 300 yards.  I shoot 75 grains of 2F in my 50 caliber flintlock for most off hand work.  I usually increase that to 85 grains for 100 yard targets.  The guy who made my rifle machined a sight that I bedded to fit in front of the rear sight to allow me to shoot at 200 yards.  With the increased height of the snap on rear sight and the altered trajectory, I had to drop the charge to 65 grains to hit a gong at 200 yards.  It was pretty consistent if the wind was still.  At 200 yards we would get 2 to 3 feet of drift with almost any breeze.  Fortunately there was a white rock on the berm that was upwind and a perfect hold.  You could almost eat a snack waiting for the gong to ring.  I believe there is an optimum spin rate for a round ball of any diameter, although that varies with mass.  That can be achieved with fast twist or heavy powder charges (a faster trip down a slower twist barrel), either of which could achieve that spin rate.

[Daryl]

This sight, is filed-in and regulated for 100, 150, 200 & 300 meters in 1986.
 
I filed it in for 165gr. 2F GOEX, a .682" pure lead ball and 12 ounce (.030") denim patch.



This is the front sight, unchanged since 1986.

[Dphariss]

1 in 48 is perfect for all calibers. Westerners may disagree as they tend to shoot longer distance for hunting

.

I agree with enthusiasm, but over 62 cal. 66-72” might be better. The larger balls have much more rotational inertia and don’t like to spin up..
I have a 67 cal 80” twist that shoots great with 140 gr of FF Swiss. This BTW is less than 1/3 ball weight. This equates to about 17 gr if it were a 32. 
This makes 1600 fps. And with “Forsythe” narrow lands, shallow grooves about .008, it shows a little wear on the patches at the lands. Think it would be better with maybe 10 grooves..

[Dphariss]

I once had a Sharon Hawken with 72 twist and it needed 120 to shoot accurately. I think the 66-72 twist found on many modern barrels is too slow unless the bore is larger than the norm. I would bet that most colonial/transitional kentuckys were about 48 twist which figures with the European practice of one turn in the barrel length given the “4 ft” barrels.
But as someone pointed out RBs don’t much care.