Accuracy with a round ball is based on a paradox; an undersized ball is spun by the riflings of a muzzleloader it never touches.
To do this, we must look at the cloth patch.
It functions as a gas seal "theoretically", plus transfers the rate of spin to the ball from the rifling.
To perform it's double duties, the cloth patch should fill the grooves of the rifle, in other words, it must be under great compression at the lands as well as the bottom of the grooves. a tight fitting combination of both patch and ball is an absolute must for accuracy.
However, while a tight fitting combination of both patch and ball is the answer to accuracy, it cannot be carried to an extreme. If the fit is too tight, the front of the projectile becomes distorted during the loading process and the ball will not fly true.
A compromise between loadability and bore sealing must be reached...
Measure both the bore and grooves of your rifle with a micrometer, or slug your barrel by driving soft lead through the length of the bore. (once the breech plug has been removed)
Subtract the bore diameter from the groove diameter and divide by 2... This will give you the depth of the riflings. (groove depth)
The thickness of your patch is directly related to the depth of the riflings.
EXAMPLE:
groove diameter = .4654
bore Diameter = .450
divide by 2
.4654 - .450 = .0154 / 2 = .0077
(round up to .008) This is the maximum we can go on a round ball and minimum on a patch for this bore to seal.
So, we are using a .440 round ball in the EXAMPLE muzzleloader, and we know that the bore is .4654 diameter from our slug measurements, now it is just a matter of some simple math to figure out our patch thickness.
Therefore, .4654 bore - .440 rb = .0254 / 2 = .0127 patch size...
We can round it up for some compression and use a .013 - .015 patch with this size round ball.
Most newer muzzleloaders will come with this information supplied in the form of a loading book, with older guns that have unknown rifling depths, this formula will come in handy.
To do this, we must look at the cloth patch.
It functions as a gas seal "theoretically", plus transfers the rate of spin to the ball from the rifling.
To perform it's double duties, the cloth patch should fill the grooves of the rifle, in other words, it must be under great compression at the lands as well as the bottom of the grooves. a tight fitting combination of both patch and ball is an absolute must for accuracy.
However, while a tight fitting combination of both patch and ball is the answer to accuracy, it cannot be carried to an extreme. If the fit is too tight, the front of the projectile becomes distorted during the loading process and the ball will not fly true.
A compromise between loadability and bore sealing must be reached...
Measure both the bore and grooves of your rifle with a micrometer, or slug your barrel by driving soft lead through the length of the bore. (once the breech plug has been removed)
Subtract the bore diameter from the groove diameter and divide by 2... This will give you the depth of the riflings. (groove depth)
The thickness of your patch is directly related to the depth of the riflings.
EXAMPLE:
groove diameter = .4654
bore Diameter = .450
divide by 2
.4654 - .450 = .0154 / 2 = .0077
(round up to .008) This is the maximum we can go on a round ball and minimum on a patch for this bore to seal.
So, we are using a .440 round ball in the EXAMPLE muzzleloader, and we know that the bore is .4654 diameter from our slug measurements, now it is just a matter of some simple math to figure out our patch thickness.
Therefore, .4654 bore - .440 rb = .0254 / 2 = .0127 patch size...
We can round it up for some compression and use a .013 - .015 patch with this size round ball.
Most newer muzzleloaders will come with this information supplied in the form of a loading book, with older guns that have unknown rifling depths, this formula will come in handy.
