Understanding the different rate of barrel twists and most compatible projectiles

[Patched]

I wonder what would happen if a barrel company came out with a .54 groove diameter barrel with a 1:75 twist rate. My guess is, no one would buy it, even though, that would probably be the optimum twist rate for PRB at that caliber.

In the “ Heyday Hawken Revival Years” (1980s early 90s) 1:75 twist 54 cal barrels were offered by top makers Don Getz, “Hoppy Hopkins, Jim Goodein…I have one of each of these makers…
All are ”as good as it gets” RB shooters, for accuracy, smooth consistent bores…with the heaviest charges of powder, a felt wad and a tight weave patch….the deep rifling and slow twist accommodates the 120-140 gr powder charge as long as you protected the patches from the flame.

Flattening the trajectory of a 220 gr RB has its advantages in the field in open western terrain…the gain is real but sectional density is what actually delivers the goods…RBs have the lowest possible SD so pushing it 25% faster with 40% more powder in the 1:75 twist only turns your 100yd mule deer gun into a 150 yd mule deer gun…and it’s launched RB is gonna need to land in the exact right 8 inch kill zone.

My obsolete gen 1 CVA Optima 45 cal delivers about twice the kinetic energy at 200yds with the same 220gr weight projectile as my slow twist 535 RB does at 100yds…sighted in at 200 yds it’s only 4.5 inches high at 100yds…Those fur trappers would’ve loved to have any one of our modern in-line guns…but just like today, primers would have been scarce.
.…2cents worth of my opinion

 

[drpatton]

In the “ Heyday Hawken Revival Years” (1980s early 90s) 1:75 twist 54 cal barrels were offered by top makers Don Getz, “Hoppy Hopkins, Jim Goodein…I have one of each of these makers…
All are ”as good as it gets” RB shooters, for accuracy, smooth consistent bores…with the heaviest charges of powder, a felt wad and a tight weave patch….the deep rifling and slow twist accommodates the 120-140 gr powder charge as long as you protected the patches from the flame.

Flattening the trajectory of a 220 gr RB has its advantages in the field in open western terrain…the gain is real but sectional density is what actually delivers the goods…RBs have the lowest possible SD so pushing it 25% faster with 40% more powder in the 1:75 twist only turns your 100yd mule deer gun into a 150 yd mule deer gun…and it’s launched RB is gonna need to land in the exact right 8 inch kill zone.

My obsolete gen 1 CVA Optima 45 cal delivers about twice the kinetic energy at 200yds with the same 220gr weight projectile as my slow twist 535 RB does at 100yds…sighted in at 200 yds it’s only 4.5 inches high at 100yds…Those fur trappers would’ve loved to have any one of our modern in-line guns…but just like today, primers would have been scarce.
.…2cents worth of my opinion

I love the fact you have the original rifles from 140 years ago and you still shoot them.

Also, ball-ets like the old Buffalo Bullets or the Hornady PA Conical will shoot well in those twists. Their length is just slightly longer than a ball but their weight is considerably more. They weigh more than 1/3rd (but slightly less than 1/2) more than a round ball.
A .490 RB weighs 177gr. A .50 Hornady PA Conical weighs 240gr.
A .530 RB weighs 224gr and the old .54 Buffalo ball-et weighed 310gr.

 

[drpatton]

WOW. It got quite in here!

 

[drpatton]

I’d be interested in this in terms of using round balls in inlines for the 4h shooting sports bc of the required 60 grain max charge. Our spin club is talking about adding black powder. It is just easier to get inlines for the kids as opposed to say a 1 in 66 Hawken

The inability to get Hawken type of rifles to teach kids is a shame. The Hawken style is 200 years old and I would think, easier to make, yet modern technology is actually cheaper by about 50%. I would abandon the Idea of PRBs in an inline and try something more adaptable to the faster 1:28 twist rate. Something like Minies, Maxi-balls or some form of longer conicals. 60 gr of BP is more than enough to push them down range..

 

[Patched]

I love the fact you have the original rifles from 140 years ago and you still shoot them.

I do not have any original rifles from 140 years ago….

I built some replica muzzleloader guns in the 1970s, 1980s and early 1990s…and 2 more last year.
These years saw an incredible growth of interest in “Hawken-esque” style half stock muzzleloaders….(especially a fanatical faction of authenticity freaks concerning the original Jake and Samuel Hawken rifles of St Louis.)
I got caught up in the muzzleloader craze of the day, not buying into the “every mountain man had a Hawken“….but I could clearly see the advantages of percussion ignition, hooked patent breeches, 1:75 twist 54s and halfstocks with barrel wedges….so I built about 5 or 6 too many for my personal use…I love em all…I even took them hunting a time or two.

 

[ETipp]

Along with twist rate, the depth of the rifling is a factor.
I have an old CVA Missouri rifle 54 caliber, 1/48 twist barrel.
It will put just about every ball in the same hole at 50 yards. I tried some 54 caliber Powerbelts and they shot like crap.
I have another rifle, same twist that won't shoot a ball worth a darn but it will shoot good with any conical.

I had an old .54 Renegade that would shoot round balls very accurately but not shoot Maxi Balls well. Go figure!

Yet I'm still finding information on some long rifles that have faster twists than 1:60 or 1:66. Those are said to be very accurate with round balls. So, it must be true that depth of rifling can have a profound effect on this.

 

[Steelheader323]

I have a handful of muzzleloaders and have shot a multitude of different projectiles in them.. my go to hunting sidelock is a renegade .50 and I have shot round ball, heavy conicals, and even saboted loads in it..with the right powder charge, over powder wad setup, patch setup..it will Shoot them all Fairly well. Even a few if my 1-28” guns have shot round all well at moderate powder charges at the range..it’s all About the recipe

 

[drpatton]

I had an old .54 Renegade that would shoot round balls very accurately but not shoot Maxi Balls well. Go figure!

Yet I'm still finding information on some long rifles that have faster twists than 1:60 or 1:66. Those are said to be very accurate with round balls. So, it must be true that depth of rifling can have a profound effect on this.

Depth of rifling keeps the very maluable lead within the grooves. The faster the twist, the deeper the grooves must be.

 

[ETipp]

Depth of rifling keeps the very maluable lead within the grooves. The faster the twist, the deeper the grooves must be.

Ah, didn't know that.

 

[drpatton]

Ah, didn't know that.

Then stand edumacated ;-)

Basically, I said that because people are having a hard time understanding, a fast twist doesn't directly correlate to accuracy, especially with Round Balls. But, they are willing to give up forward velocity and groove depth to make it work.

 

[drpatton]

Using the Greenhill Formula

(Dr George Greenhill was the Mathematician who created the formula to calculate the best rifling twist rates in rifles. It is still today, being used by industry.)

Round ball twist Rates (with my preference in parentheses, which take into account of bullet obturation in the barrel and a little additional spin for minor bullet aberrrations and abnormalities.)

45 Caliber using a .440 RB is: 1:66 (1:60)

50 Caliber using a .490 RB is: 1:73 (1:65)

54 Caliber using a .530 RB is: 1:79 (1:70)

I wouldn't loose sleep over a twist slightly greater than these.

 

[GBG]

And all this math is fun, but the rpm is going to vary wildly with the velocity, so I don't think anyone should use these for more than a rough guide for selecting your starting points.

I'd been waiting for someone to mention rotational speed, RPM or RPS (revolutions per second) which is the key to stability once the bullet is in the air. RPS is determined by rate of twist and muzzle velocity.

I'm not familiar with the intricacies of bullet aerodynamics, just aware that they exist. The RB is probably the simplest of all bullet shapes, but it has one characteristic that really puzzles me. For any given diameter ball, there seems to be a rather narrow range of RPS that provides the best stability and accuracy, whether the ball is traveling 800 fps or 2000 fps.

That's why short barreled, low velocity pistols need a fast twist and high speed longrifles need a slow twist. For example:

A .50 caliber pistol with an MV of 800 fps needs a twist of at least 1:28, as deermanok pointed out in post number 15.
(800 ft/sec) X (12 in/ft) = 9600 in/sec
(9600 in/sec) / (28 in/rev) = 342 rev/sec or 342 RPS

A .50 caliber 42" long rifle with an MV of 2000 fps needs a twist of about 1:66.
(2000 ft/sec) X (12 in/ft) = 24,000 in/sec
(24,000 in/sec) / (66 in/rev) = 363 rev/sec or 363 RPS

The .50 caliber RB's speed has been increased by a factor of 2.5 (and gone from subsonic to supersonic air flow) but the RPS for good accuracy is virtually unchanged. For a .50 caliber RB roughly 350 RPS seems to be the optimum rotational speed for the best stability and accuracy regardless of MV (that can be produced with black powder).

This may go against 'common sense' but it is a fact.

 

[drpatton]

I'd been waiting for someone to mention rotational speed, RPM or RPS (revolutions per second) which is the key to stability once the bullet is in the air. RPS is determined by rate of twist and muzzle velocity.

I'm not familiar with the intricacies of bullet aerodynamics, just aware that they exist. The RB is probably the simplest of all bullet shapes, but it has one characteristic that really puzzles me. For any given diameter ball, there seems to be a rather narrow range of RPS that provides the best stability and accuracy, whether the ball is traveling 800 fps or 2000 fps.

That's why short barreled, low velocity pistols need a fast twist and high speed longrifles need a slow twist. For example:

A .50 caliber pistol with an MV of 800 fps needs a twist of at least 1:28, as deermanok pointed out in post number 15.
(800 ft/sec) X (12 in/ft) = 9600 in/sec
(9600 in/sec) / (28 in/rev) = 342 rev/sec or 342 RPS

A .50 caliber 42" long rifle with an MV of 2000 fps needs a twist of about 1:66.
(2000 ft/sec) X (12 in/ft) = 24,000 in/sec
(24,000 in/sec) / (66 in/rev) = 363 rev/sec or 363 RPS

The .50 caliber RB's speed has been increased by a factor of 2.5 (and gone from subsonic to supersonic air flow) but the RPS for good accuracy is virtually unchanged. For a .50 caliber RB roughly 350 RPS seems to be the optimum rotational speed for the best stability and accuracy regardless of MV (that can be produced with black powder).

First, rps is dependent on velocity. The faster an object goes, the more rotation is required to stalize it. This may go against 'common sense' but it is a fact.

RPM or RPS is dependent on velocity. The faster an object moves the more rotation is required to stabilize it. Which is exactly what happens when a bullet travels faster. The rotational velocity increases. The amount of turns per inch are the same; However, the number of rotations per second have increased. So, since the RPS have increased or decreased as needed with velocity, all is fine.

There is a differnce in twist rates for Handguns and rifles. Rifles, which are more inherently accurate, use the twist for accuracy. Hanguns use it for stability within a smaller distance, because they are not as accurate. So don't get caught up in apples and oranges argument on that.

Now, as far as the formula:
Dr Greenhill was a mathematician who came up with this formula, which is still used. It has to be accurate or firearms manufacturers would have abandoned it long ago. Also, this is a rule of thumb. It gets you into the ballpark. Actually, it gets you into the infield. Now, a munitions manufacturer, like Hornady or Remington would use the Miller Test, but we don't need to get that far down into the weeds. The numbers I gave are correct. One can argue over a few inches per twist (1:70 vs 1:72), but this is essentially correct.

https://en.wikipedia.org/wiki/Alfred_George_Greenhill
There is also the Miller Test Rule; However, since we are dealing with lead only, Greenhill's formula works great and it is pretty accurate. Miller deals with alloys and copper jackets, so bullet weight is used as well as mass. (Mass is density within a given volume, where weight is independent of volume.) Since lead's weight and mass are consistant, there is no need to deal with any of this.

If you worked out the formula both ways, with our larger bores, you come up within a fraction of an inch. The difference really shows up with small calibers with high velicity. Also, note Greenhill uses a standard velocity index of 150 for lower velocities (under 2,800' per second) whereas Miller is precise .

https://en.wikipedia.org/wiki/Miller_twist_rule

Barrel Rifling 101: Types, Twist Rates, and More​

https://gununiversity.com/barrel-rifling-101/

 

[drpatton]

Dr Greenhill was a mathematician who came up with this formula, which is still used. It has to be accurate or firearms manufacturers would have abandoned it long ago.

https://en.wikipedia.org/wiki/Alfred_George_Greenhill
There is also the Miller Test Rule; However, since we are dealing with lead only, Greenhill's formula works great and it is pretty accurate. Miller deals with alloys and copper jackets, so bullet weight is used as well as mass. (Mass is density within a given volume, where weight is independent of volume.) Since lead's weight and mass are consistant, there is no need to deal with any of this.

If you worked out the formula both ways, you come up within a fraction of an inch.

https://en.wikipedia.org/wiki/Miller_twist_rule

I'd been waiting for someone to mention rotational speed, RPM or RPS (revolutions per second) which is the key to stability once the bullet is in the air. RPS is determined by rate of twist and muzzle velocity.



This may go against 'common sense' but it is a fact.

I'd been waiting for someone to mention rotational speed, RPM or RPS (revolutions per second) which is the key to stability once the bullet is in the air. RPS is determined by rate of twist and muzzle velocity.



This may go against 'common sense' but it is a fact.

I'd been waiting for someone to mention rotational speed, RPM or RPS (revolutions per second) which is the key to stability once the bullet is in the air. RPS is determined by rate of twist and muzzle velocity.

I'm not familiar with the intricacies of bullet aerodynamics, just aware that they exist. The RB is probably the simplest of all bullet shapes, but it has one characteristic that really puzzles me. For any given diameter ball, there seems to be a rather narrow range of RPS that provides the best stability and accuracy, whether the ball is traveling 800 fps or 2000 fps.

That's why short barreled, low velocity pistols need a fast twist and high speed longrifles need a slow twist. For example:

A .50 caliber pistol with an MV of 800 fps needs a twist of at least 1:28, as deermanok pointed out in post number 15.
(800 ft/sec) X (12 in/ft) = 9600 in/sec
(9600 in/sec) / (28 in/rev) = 342 rev/sec or 342 RPS

A .50 caliber 42" long rifle with an MV of 2000 fps needs a twist of about 1:66.
(2000 ft/sec) X (12 in/ft) = 24,000 in/sec
(24,000 in/sec) / (66 in/rev) = 363 rev/sec or 363 RPS

The .50 caliber RB's speed has been increased by a factor of 2.5 (and gone from subsonic to supersonic air flow) but the RPS for good accuracy is virtually unchanged. For a .50 caliber RB roughly 350 RPS seems to be the optimum rotational speed for the best stability and accuracy regardless of MV (that can be produced with black powder).

This may go against 'common sense' but it is a fact.

I'm going to lay out an example.

Let us say we have a barrel with a twist of 1:36". We fire a rifle and the bullet travels that distance in 1 second (it's slow burning powder). The bullet has made 1 rotation in 1 second. Now, let's increase the charge and the bullet travels 72" in 1 second. The amount of rotations per second have doubled, yet the rotations per 36" stays the same.
Velocity or speed is = to the distance traveled / time.
So as speed or velocity increases, so do the number of rotations per second. Yet for every given set distance, 36" per my example, the number of rotations stay the same.

Lay out 144 inches in 1/4 increments (36"). If the bullet travels 36" per second, then the rotation is 1 rps. Increase the velocity by 100% and the bullet has traveled 72" in 1 second which gives us 2 rotations per second. Double the velocity again and we travel 144" in 1 second, which gives us 4 rotations per second. Bullets need more rotations per second to stabilize at higher velocities, yet that is exactly what occurs. The faster the bullet travels the more rotations per second it has.

 

[Greg_E]

Here is a Miller calculator to take the math out of the process. My example with the 45 REAL above works under a 1:60 barrel but not a 1:66 and I truly don't remember which twist it has. For anyone shooting spire points with plastic ballistic tips, this might be useful. Though I'm guessing people who are shootIng these types of rounds will be using an inline with probably a much faster twist like 1:30 or 1:24 which will stabilize a much longer bullet.

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi
(edit) I just checked a .490 round ball, and with a 1:66 it shows a marginal stability at 1500fps. Greenhill calculates a 1:72 for the same which should make the 66 plenty stable.

 

[drpatton]

Here is a Miller calculator to take the math out of the process. My example with the 45 REAL above works under a 1:60 barrel but not a 1:66 and I truly don't remember which twist it has. For anyone shooting spire points with plastic ballistic tips, this might be useful. Though I'm guessing people who are shootIng these types of rounds will be using an inline with probably a much faster twist like 1:30 or 1:24 which will stabilize a much longer bullet.

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi
(edit) I just checked a .490 round ball, and with a 1:66 it shows a marginal stability at 1500fps. Greenhill calculates a 1:72 for the same which should make the 66 plenty stable.

I think you are missing the point. There is a difference in stability versus accuracy. Stability is the faster an object rotates, the more stable it becomes. This is called the "gyroscopic" effect.

Accuracy requires stability, up to a point. There is what is called a point of "diminishing returns." The mathematical term is, it hit its "limit." What this means is for accuracy, once a bullet is stable, making it more stable doesn't give more accuracy in return. In fact, with lead in muzzleloaders, (as with any bullet, really) the bullet can't keep up with the attempt to add more stability. It starts stripping or tripping through the rifling. This is why people use the Greenhill formula over the Miller. Miller is for more for alloys and jacketed bullets.

For some reason, which I don't know, handguns try to make a bullet more stable but not more accurate.

I hope this helps.

 

[GBG]

Post number 52 was about round balls only.

There is a differnce in twist rates for Handguns and rifles. Rifles, which are more inherently accurate, use the twist for accuracy. Hanguns use it for stability within a smaller distance, because they are not as accurate. So don't get caught up in apples and oranges argument on that. . . . For some reason, which I don't know, handguns try to make a bullet more stable but not more accurate.

I think you are missing the point.

Likewise . . . WADR.

 

[Patched]

I think you are missing the point. There is a difference in stability versus accuracy. Stability is the faster an object rotates, the more stable it becomes. This is called the "gyroscopic" effect.

Accuracy requires stability, up to a point. There is what is called a point of "diminishing returns." The mathematical term is, it hit its "limit." What this means is for accuracy, once a bullet is stable, making it more stable doesn't give more accuracy in return. In fact, with lead in muzzleloaders, (as with any bullet, really) the bullet can't keep up with the attempt to add more stability. It starts stripping or tripping through the rifling. This is why people use the Greenhill formula over the Miller. Miller is for more for alloys and jacketed bullets.

For some reason, which I don't know, handguns try to make a bullet more stable but not more accurate.

I hope this helps.

Benchrest shooters and accuracy fanatics seem to lean towards an absolute minimum twist for specific bullet lengths/designs…they’re concerned with .015“ of group size…but they reveal a secret for accuracy…which I interpret as “use the minimum twist needed“ to stabilize what ever projectile you’re shooting.

Round balls have the least requirement for spin stabilization and the least amount of bearing surface available for gripping the rifling…which I interpret as “use deep cut rifling at a very slow rate of twist”.

In practicality accuracy is maintained over a wider range of powder charges…including large charges…according to my experiences.

 

[drpatton]

Post number 52 was about round balls only.





Likewise . . . WADR.

My apologies. I was trying to figure out where you were coming from. Some people believe the faster twist means better accuracy, which isn't true. In fact, it can man the opposite. They then point out to handguns, which do use a faster twist, but it isn't for accuracy. It's for stability.

As Patched said, "Benchrest shooters and accuracy fanatics seem to lean towards an absolute minimum twist for specific bullet lengths/designs." This is absolutely true.

As far as your REAL bullets, I don't know. It may have to due with bearing surface..

 

[drpatton]

Post number 52 was about round balls only.





Likewise . . . WADR.

Rifles are inherently more accurate. That doesn't mean you can't find a person who can shoot a revolver and make shot few others can not.

Rifles are inherently more accurate due to barrel length, sight radius, powder effeciency in the longer barrel, etc. How many handguns can make 300 yrd shots and how many rifles can. How many handguns can shoot MOA? Thompson Center "Renegades" were known to right out of the box.