Why is a fast twist bad for a round ball?

[hung load]

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?

 

[roundball]

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?

A slower twist for round balls normally gives optimum accuracy for a round ball, and given a choice, would probably be best for someone interested in competition shooting, measuring group size with a micrometer, etc.

That does not mean that a 1:48" twist is inaccurate with round balls as is often suggested...ie: there's an old wives tale circulating around which has become oversimplified and incorrectly states that 1:48" twists don't shoot round balls accurately"...that is simply not a true statement on it's face...it's a matter of degree, and a relatively small degree at that.

As a good example, someone has recently posted, a 1:66" made a single ragged hole for him about 1" size, and the 1:48" made a 1.5" size group...obviously very little difference, unless interested specifically in precision match shooting, etc.

The benefit of the 1:48" design is that it also normally shoots larger conicals pretty well too, where the slower round ball twist usually does not do as well with conicals.

I've got both 1:48" and 1:66" barrels, in different calibers, shoot them all, and while there's a marginal difference towards tighter round ball groups with a slower twist, it is misleading to make a flat statement that "1:48" barrels do not shoot round balls accurately".

 

[davy]

I believe it all comes down to contact area on the projectile. A round ball has very little contact area other than the specific outer diameter of the circumfrance of the ball ... the faster the twist as it is moving down the barrel, the greater the chance of lost contact, such as stripping the ball of its contact surface.

A longer projectile on the other hand has many times more surface contact area in the barrel due to its longer length and contact area, with the accompanying result of less loss of said contact as the bullet traverses the barrle tube, in relation to the twist, so as a result, less chance of stripping ocurring.. At least that the way I see it!

You could offset the twist issue somewhat with a deeper groove to give more bite and contact area to the roundball. This is what I think is true of many of the older barrels. :hmm:

Davy

 

[roundball]

You could offset the twist issue somewhat with a deeper groove to give more bite and contact area to the roundball.

Agree...and is probably why a tight patch/ball combo when using heavy hunting charges in the moderate 1:48" twist seems to produce good accuracy, gripping the lands better, etc.

 

[Stumpkiller]

Speed is also a factor. A light round ball load for a given caliber may perform better with the faster twist. My 1:48" twist .50 T/C New Englander hates anything over 95 gr of 2F but will punch one hole at 50 yards with 80 and below. I used to think I needed 100 gr for deer, but I've learned better in my old age. Now I use low 80's in all my .50's and .54's. I use a .45LC case full of powder (42 gr FFg) for squirrel and take only head shots. Don't tell me a 1:48 is inaccurate ~ when it's "faults" are catered to.

Some slow bored rifles prefer more-than-moderate loads for best performance. The 1:48" is a middle of the road compromise for multiple projectile choices.

 

[chickenlittle]

The two main theories are flight stability and jumping the rifling.

A given project has stable flight at a some spin range. The rifling twist rate and the muzzle velocity gives the spin. To get the same spin of your round ball, your load is decreased going from a slow twist rifling to a fast twist. A pistol is normally given a fast rifling twist since it can't reach the same MV as a long rifle. For a long conical bullet, more spin is needed to stabilize it so fast twists are better (and MV is lower than for a RB).

The alternative explanation is that the ball travels down the barrel too fast to follow the rifling and accuracy drops off. So you can shoot a ball faster through a slow-twist barrel than a fast twist.

Your rifle may disagree with this convention wisdom.

 

[jtmattison]

I have a 1:48 twist Trade Rifle that shoots roundball far better than any conical I have stuffed into it.
My 1:60 twist GPR shoot roundball even better because that is what it's made for.
My 1:32 twist GPH shoots several conicals with superb accuracy.
Twist makes all the difference. Choose your projectile accordingly.
There are also those rifles that will shoot roundball well out of fast twist and conicals out of slow twist.
Experiment and find out what yours likes.

Huntin Dawg

 

[stewarttls]

I always try to compare the fast twist for prb just like a pitcher throwing a curve ball-The more the twist (wrist action) the bigger the curve-Might not be right, just always come to mind

Tommy From Northeast Texas

 

[TANSTAAFL]

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.

 

[Runner]

I believe it is stripping over the top of the rifling with heavy loads that bites the faster twists. Having said that, I have to say this. I have a CVA 1-32 barrel here that I hunted squirrels with using 70 grains of 3f 777 under a 495 roundball. I never did any grouping tests, but if you missed a squirrels head at 50 yards, it was wasn't the guns fault. As several others have said here, I think the way the rifling is cut, how deep it is, and how tight a load you are shooting all make a difference with the 1-48 guns. I shoot 70 grains of 3f Goex at deer usually, so that squirrel load was hotter than the one I normally shoot in my slower twist guns. The subject is not as simple as slow for ball and fast for conical, light load for fast and heavy load for slow, but those rules make a very good starting point.

 

[rice1817]

I had a long talk withBruce at[url] Underhammers.com[/url] about this. I wanted to know why the Zephyr rifles have that extremely slow twist. He told me it was so that one can pour humongous charges of powder in them to get the huge balls to fly with a reasonably flat trajectory. It actually has a lot to do with the RPMs needed to stabilize a round ball. RPM is a function of velocity and barrel twist. The faster twist rifles will shoot roundballs effectively at slower velocities, the slow twist barrels will shoot effectively with much higher velocities. About 300-400 Revolutions per second seems to be the magic number. Some of the old European built jaegers had very fast twists by our roundball standards. That is because they shot large balls at a slow velocity for their short range work. I did an extensive spread sheet on it and sure enough, the big bore zephyrs with their 1:104 twist need to get up to about 1700 fps to hit the required RPS figure to stabilize the big ball. But, that is what they are made for, maximum muzzleloading roundball power. ( He recommended a 1:48 twist .62 barrel with 90 grains, 1400 fps as a comfortable, accurate load that will kill anything that walks in the Pa. woods). He said I would need 120 grains or more in a 1:66 to get any kind of accuracy, and that would not be a load that one would want to shoot for extended sessions.

 

[Zonie]

My thoughts on fast twist barrels:
I think the main reason the fast twist barrels have a reputation for poor shooting with a round ball is most of the modern fast twist barrels have very shallow rifleing depths.

The original large bore Hawkens used a 1:48 twist and were noted for their accruacy. They also had deep grooves.

I feel that deep grooves are needed to prevent the patch from skipping or slipping when heavy loads are used.

Looking at some of the old and new barrels made for shooting round ball I see rifleing depths like .008-.015 . Some old guns have even deeper rifleing grooves.

Looking at some of those modern muzzleloader things I see things like 1:38 twist, .005 groove depth, 1:28 twist, .005 groove depth.
While .005 deep grooves work well with sabots and solid lead slugs, they don't have much grabbing power on cloth. Remember, .005 is less than the thickness of two pieces of paper.

As was mentioned earlier in this post, the sphere has the smallest contact area with the barrel of any form.
This small contact area, coupled with very shallow grooves in modern fast twist barrels can result in the patch and ball slipping.
The slipping in turn can cause the patch to tear and/or blow thru in localized areas releasing the powders gas pressure in unpredictable directions. This in turn can deflect the ball away from the point of aim and teach you new creative ways of using old Anglo-Saxon words.

 

[shmrck1]

Zonie,
I must say that in the past I have not
given groove depth much attention. However what
you say makes great sence.
Thank for the post
snake-eyes :hatsoff:

 

[hung load]

Thank you to all who have replied to my question. Some fascinating reading that is beginning to help me understand the intricacies of BP. :hatsoff:

 

[walruskid1]

hang in there hung load, after 30 or 40 yrs it starts to make sense. :hmm:

 

[TANSTAAFL]

When it comes to front stuffers, rock locks and such, if you are not in a perpetual state of confusion, you are not shooting or building them.

 

[Pilot Point]

In the only old hotel in Cooperstown upstate NY, in their bar room, there was an original Jaeger flinter hung over their stone fireplace - bore was around .75 with an 11 groove rifling, shaped like a star at the muzzle, deeply tapered like a funnel for ease of loading.

It had very deep ' V ' shaped grooves around 1/32 " deep or more like 1/16". I kid you not. I was told by an old bartender who had worked there 40 years, this was 1960s, that when he was growing up around Cooperstown, the old timers used to shoot that old Jaeger every Octoberfest in a contest. Bartender said 20 or 30 shots were required timed in 10 minutes or so (he didnt remember exact time limit) and they never had to clean "... the sooty old thing..." at any time during 20 - 30 shots.

The deep ' V ' shaped grooves never fouled enough to prevent loading. He said more than half the contests were won by that old Jaeger. Had a rather short barrel. I remember being surprised at that. Up until then I thought all old flinters had only long barrels.

Anyone who's fired more thar 7 or 8, 3 dram loads of bp in a shallow grooved reproduction flint or cap lock will catch my meaning. Deep grooves and bp work well together. All this talk of spin rate and high velocity heavy charges has a lot of truth in it. But try the varients with very deep groove rifling and the spread of differences in the varient factors might narrow alot. I'd bet a few tankards of Jaegermeister that it would.

 

[yonderin]

All I can say is that a longer (and therefore heavier) projectile, FOR THE SAME CALIBER, requires a faster twist to stabilize it. 1 in 48 is a compromise which allows both round ball and boolits to work reasonably well. Although not ideal for either. I have a theory that by playing with velocity, the spin rate can be somewhat compensated for, although I've never really tried to prove it.

Internal ballistics is a bit of a science.

 

[SDSmlf]

All I can say is that a longer (and therefore heavier) projectile, FOR THE SAME CALIBER, requires a faster twist to stabilize it. 1 in 48 is a compromise which allows both round ball and boolits to work reasonably well. Although not ideal for either. I have a theory that by playing with velocity, the spin rate can be somewhat compensated for, although I've never really tried to prove it.

Internal ballistics is a bit of a science.

Believe many of the Hawken brother’s guns as well as others had a 1-48 twist. There were other guns had twist of one revolution per the length of the barrel. Most, if not all, were intended for roundball use in their day. The caliber and depth of the rifling plays a big roll, deeper rifling being more suited for patched roundballs. A 62 caliber with a 1-48 to 1-60 twist may shoot roundballs fine over 80-100 grains of powder. Slow that twist down to 1-72 and it may require 150 grains of powder to get optimum accuracy. The ‘compromise twist’ was a great marketing ploy by companies like Thompson Center, and at best, the only science was ‘marketing science’.

 

[Britsmoothy]

Believe it or not but some thing's can be over spun so that they end up being unstable.
The shorter the length of a missile the less it needs to spin to become gyroscopically stable along its axis.
It has nothing to do with skipping over the lands, that's what the patch is for.

Modern bullets don't skip shallow rifling under much more stress by thousands of times.
RPM and velocity ranges play an important role in the equation for optimum spin, that and bullet length.
Balls being the shortest require the lowest RPM to become stable on an axis.
As a side not for certain modern cartridges the industry standard for rifling twist is for some out of date. With many lands moving away from lead cored bullets the new bullets are often longer compared to bullets of yesteryear and thus need a faster twist.
The faster twists for muzzleloaders are for conical bullets. If it's a compromise thing then there will be a compromise in performance somewhere.