Barrel twist for deer hunting
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Ditt44
40 Cal
I found a T/C White Mountain fast-twist flintlock barrel and put it on a factory-second stock that I had finished. It is a Hawken version which I hacked off the fore-end cap and sort of gave it a Renegade look. Two reasons for that: the wood was split near the top left end of the barrel channel and I did not want to cut the barrel under rib.
I was surprised to find how well it shot round balls. I started at 40 grain of 3F and worked up to 70. It is an easy two inch group at 50 yards with 70 grains 3F, a .490 ball and .015 patch. I am yet to try the .018 ticking in it but see no need to worry about it so far. With my eyes, I'm thrilled to see it shoot that well.
I was surprised to find how well it shot round balls. I started at 40 grain of 3F and worked up to 70. It is an easy two inch group at 50 yards with 70 grains 3F, a .490 ball and .015 patch. I am yet to try the .018 ticking in it but see no need to worry about it so far. With my eyes, I'm thrilled to see it shoot that well.
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My own anecdotal experience agrees with you. I shoot a TC .50 1:48 26" BBL. I had trouble dialing it in with thin patches, but once I started using thicker patches it got better. My go to target load is .490 ball, 55gr 3F, .020 patch, and my homebrew lube (soap/oil blend) and it's accurate enough for me to win the occasion prize at a woods walk.
It is tight, I stopped using a normal short starter and use one I made like a mallet to tap it into the bore and save my palms.
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There is good practical information in this thread...
Here is the scientific explanation (that also happens to be 100% true practically).
A sphere is an exceedingly bad projectile for flying through the air. It creates a great deal of friction at the front and a big vacuum behind it when it leaves the barrel that is akin to a drag racer standing on the brakes ten feet from the start line. However, it is the most stable projectile there is. Nothing is as stable as a sphere. Any slight twist at all 100% stabilizes it, and it's pretty darn stable as a knuckle ball which is why smooth bores work.
a 270gr round ball has about 1/3 the ballistic coefficient of a 40gr, .22 Spitzer conical. Simplified, if it helps you think about it this way, it slows down three times as fast. This is why the only solution to raising the BC on a round ball and getting more range was to go larger and heavier (or shoot a projectile more dense than lead). The longer and more aerodynamic the projectile the higher it's BC, but the more unstable it becomes and the faster you need to spin it to keep it from yawing in flight.
Here is a black powder solver you can play with and input different muzzle velocities to see how they fly (its bad).
https://www.ctmuzzleloaders.com/ctml_experiments/rbballistics/rbballistics.html
When a bullet slows down from super sonic to transonic the transition destabilizes most bullets and especially the long Very-Low-Drag bullets with high BCs favored by todays marksmen. A round ball is so stable it doesn't even notice going transonic. This is why a typical deer load is slowing down so fast it goes transonic at under 100 yards, yet this doesn't effect precision. Where a modern high power 6mm will hold a trajectory out to say, 1200 yards, but once it drops below 1,125 Fps it tumbles and is all over the place.
Calculating the bullet stability requires another solver. Berger makes a good one.
https://bergerbullets.com/twist-rate-calculator/
If you know what bullets you are going to be shooting you can order a barrel with the correct twist rate to fully stabilize them. This is pointless with round balls. Mathematically they are already 100% stable with no twist. The twist just irons out the reality that they aren't "perfect" spheres. All bets are off when you go conical. Now you have to stabilize the bullet in flight. The weight, shape, and speed of the bullet all enter into it. Generally the more of those three the more twist it needs to stabilize. For instance, something like a .220 Swift is throwing a 30gr Spitzer (flat back) bullet at 3,800 Fps, but it only needs a 1/20 twist because it's so light and fast, but the BC is so low that it goes transonic at about 450 yards; whereas my .300 WM is throwing 230gr Juggernauts @ 1,750Fps and needs a 1/6.5 twist to maintain stability out to about 1,800 yds before it goes transonic and falls apart.
There is no evidence, on paper or practically, that you gain anything by spinning a round ball any faster than 1/72. At the same time, there is also zero downside till you spin it so fast it flies apart, which is probably impossible with a patch. If you go conicals for a longer effective range all this comes into play. If you shoot round balls it is almost irrelevant. If you want a greater effective range you have to go bigger. When I started this I thought .50 cal was huge. It's tiny. If you want to shoot BP "long range" you need to be throwing much bigger pills than a 270gr RB.
Ballistics are kewl.
Here is the scientific explanation (that also happens to be 100% true practically).
A sphere is an exceedingly bad projectile for flying through the air. It creates a great deal of friction at the front and a big vacuum behind it when it leaves the barrel that is akin to a drag racer standing on the brakes ten feet from the start line. However, it is the most stable projectile there is. Nothing is as stable as a sphere. Any slight twist at all 100% stabilizes it, and it's pretty darn stable as a knuckle ball which is why smooth bores work.
a 270gr round ball has about 1/3 the ballistic coefficient of a 40gr, .22 Spitzer conical. Simplified, if it helps you think about it this way, it slows down three times as fast. This is why the only solution to raising the BC on a round ball and getting more range was to go larger and heavier (or shoot a projectile more dense than lead). The longer and more aerodynamic the projectile the higher it's BC, but the more unstable it becomes and the faster you need to spin it to keep it from yawing in flight.
Here is a black powder solver you can play with and input different muzzle velocities to see how they fly (its bad).
https://www.ctmuzzleloaders.com/ctml_experiments/rbballistics/rbballistics.html
When a bullet slows down from super sonic to transonic the transition destabilizes most bullets and especially the long Very-Low-Drag bullets with high BCs favored by todays marksmen. A round ball is so stable it doesn't even notice going transonic. This is why a typical deer load is slowing down so fast it goes transonic at under 100 yards, yet this doesn't effect precision. Where a modern high power 6mm will hold a trajectory out to say, 1200 yards, but once it drops below 1,125 Fps it tumbles and is all over the place.
Calculating the bullet stability requires another solver. Berger makes a good one.
https://bergerbullets.com/twist-rate-calculator/
If you know what bullets you are going to be shooting you can order a barrel with the correct twist rate to fully stabilize them. This is pointless with round balls. Mathematically they are already 100% stable with no twist. The twist just irons out the reality that they aren't "perfect" spheres. All bets are off when you go conical. Now you have to stabilize the bullet in flight. The weight, shape, and speed of the bullet all enter into it. Generally the more of those three the more twist it needs to stabilize. For instance, something like a .220 Swift is throwing a 30gr Spitzer (flat back) bullet at 3,800 Fps, but it only needs a 1/20 twist because it's so light and fast, but the BC is so low that it goes transonic at about 450 yards; whereas my .300 WM is throwing 230gr Juggernauts @ 1,750Fps and needs a 1/6.5 twist to maintain stability out to about 1,800 yds before it goes transonic and falls apart.
There is no evidence, on paper or practically, that you gain anything by spinning a round ball any faster than 1/72. At the same time, there is also zero downside till you spin it so fast it flies apart, which is probably impossible with a patch. If you go conicals for a longer effective range all this comes into play. If you shoot round balls it is almost irrelevant. If you want a greater effective range you have to go bigger. When I started this I thought .50 cal was huge. It's tiny. If you want to shoot BP "long range" you need to be throwing much bigger pills than a 270gr RB.
Ballistics are kewl.
Grenadier 1758 is spot-on, rifling depth is the most important factor !!
During my 6 decades of collecting & shooting mostly original flint & percussion firearms designed for patched round ball featured rifling depths of .010 to .018 deep & a rate of twist averaging one-turn in length of the barrel have produced the best accuracy & groups.
Modern mass produced muzzleloading barrels such as Thompson Center with 1in 48" rate of twist are capable of excellent accuracy if the bore is measured & properly fitted with a 'tight fitting ball' & patch that is slightly thicker than the rifling depth along with a 'reasonable' powder charge.
Relic shooter.
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More powder can actually give you a better grip on the rifling because of the bump up of the bullet, aka obturation.
When you go from 50 grains to 75 grains and your group falls apart, we can theorize (with no evidence) that we're skipping the rifling and stop trying.
Or we could add even more powder and see if your groups will come back because the ball will grip the rifling better as the ball upset to fill the grooves.
I really see a problem happen with wheel weights when charges get bigger and bigger. Patches will start to blow apart with wheel weights because the ball is so hard that it will not swell to seal the barrel like pure lead will. I believe that this is more blow-by, than "skipping"
Here is a .570 pb ball that I recovered that shows a flat back ball, and you can clearly see that the ball has expanded to fully fill the rifling grooves. This is 110 grains of 3fff Swiss or Olde Eynsford. This patch/ball combination loads ridiculously easy,...so, NO, this did not occur during loading, like some might theorize.
When you go from 50 grains to 75 grains and your group falls apart, we can theorize (with no evidence) that we're skipping the rifling and stop trying.
Or we could add even more powder and see if your groups will come back because the ball will grip the rifling better as the ball upset to fill the grooves.
I really see a problem happen with wheel weights when charges get bigger and bigger. Patches will start to blow apart with wheel weights because the ball is so hard that it will not swell to seal the barrel like pure lead will. I believe that this is more blow-by, than "skipping"
Here is a .570 pb ball that I recovered that shows a flat back ball, and you can clearly see that the ball has expanded to fully fill the rifling grooves. This is 110 grains of 3fff Swiss or Olde Eynsford. This patch/ball combination loads ridiculously easy,...so, NO, this did not occur during loading, like some might theorize.
Good point Freedom, using wheel weights instead of pure lead for patched round balls is a bad idea.
Recovering fired patches is method most use to diagnose reason for poor prb accuracy & grouping.
With so many variances in bore diameters, rifling depths & rifling rates of twist,,, the only option to get off to a good start
with a new gun is to first measure the bore & rifling depth to determine the correct ball diameter & patch thickness that particular barrel requires.
Back when I was teaching muzzleloading during the 60s& 70s movies made some feel shooting 100+ grains of powder was necessary or cool.
To demonstrate a given barrel length could only burn so much powder I had them fire their excessive loads over about 30 ft. of white butcher paper
to show the unburned powder & shredded patches.
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Outstanding!!!
My shooting bag has a mallet and a furniture ball with a hole for the ramrod end. Sitting at the bench with the rifle butt on the ground with both hands on the knob makes seating the ball easy.
Can you share a pic when you get a chance? I'm having trouble visualizing but always looking for new better ways
hanshi
Cannon
Rifling twist rate depends more on caliber than anything else. AND twist rate is too often given more importance than it deserves. As long the grooves are reasonably deep anywhere from a 1-48" to 1-66" works great for round ball of .32 to 54 at least. As the caliber gets larger even slower twist rates work well.
I concur
