If you are thinking of purchasing a black powder rifle or pistol it may be smart to decide what you are going to use the weapon for before you buy it. Do you want to shoot patched roundballs or minié balls? Or perhaps both? If you don't think this though you may end up with a firearm that doesn't meet your expectations. The secret to success is often inside the barrel.

The relationship between rifling twist, rifling depth and calibre is important. The art of rifling barrels has been known for over 500 years, so it is not a modern invention. The rifling consists of several grooves that are cut as a spiral inside the barrel. The task of the rifling is to give the projectile a rotating spin in the air. The spin ensures better stability and increased accuracy. The rifling twist is perhaps the most important factor, but also the most overlooked regarding barrel selection.

There are many types of rifling. The most common is a barrel which is round internally with a square rifling profile. In quality muzzleloading barrels the squared profile is sometimes rounded to ease loading and prevent the rifling from cutting the patch. Another type of rifling is hexagonal. Inside the barrel the hexagon is cut like a spiral. This type of rifling is called Withworth rifling. The advantage with hexagonal rifling is ease of cleaning. The Norwegian Model 1860 kammerlader has Withworth rifling, while the Norwegian and Swedish 12 mm Remington rolling block rifles have a kind of Withworth rifling with round bottomed rifles in the angles of the hexagon.

In the old days the barrels were rifled in rifling benches which was a time-consuming process (see the Longrifle Project). Today few of the mass-produced black powder weapons have cut rifling. Instead the rifling is made by a button that is pulled through the barrel. This only takes a few seconds. It is difficult to make deep button rifling and that it the reason why many cheap muzzleloading rifles have rifling that is, in my opinion, too shallow.

Glossary

Rifling twist: The rifling twist is measured in how many turns the spiral of the rifling makes in a given length. 1 in 48" means that the spiral makes one full turn in 48".

Rifling depth: The depth of the grooves. See the illustration below.

Calibre or bore diameter: The bore diameter is the diameter across the rifling flats. In Europe the diameter is often expressed in millimetres, while in America it is expressed in inches. Examples: .50", 9 mm, etc. Calibre designations are often nominal. The bore diameter of a .45-70 rifle may be, for example, .458” or even .460”.

The general rule is that roundballs should have a slow twist to achieve best accuracy, while conical bullets works best with faster twists. If you use a twist that is somewhere in between you may use both roundballs and conicals. I addition, the rifling depth and number of grooves are factors that must be considered. Deep rifles work best with roundballs, while shallow rifling is best suited for conical bullets.

Some black powder rifles have fast 1:18"-1:20" twists. This applies to most Sharps and Remington rolling block replicas in .45-70 Gvt. .40 calibre rifles often have an even faster 1:16" twist. The size of the calibre influences how fast or slow the rifling should be. Small calibre weapons must have faster twist compared to large calibre weapons. An example from modern firearms: .17 Remington has 1:9" as standard while .308 Win. has 1:12".

This means that .40 and a .58 calibre rifle have different standards. Confused? See the list below for an overview.

Example: .50 calibre muzzleloading rifle

Let's use a .50 calibre muzzleloading rifle as example.

.50 calibre and patched roundballs:

As previously mentioned the grooves should be deep for best results with roundballs. The reason is that a piece of cloth is used between the ball and the barrel, and to enable the rifling to get a good grip of the patch the rifling must be deep. In a .50 calibre rifle a groove depth of .010" to .018" is suitable for roundballs.

In my opinion, the rifling twist should not be faster than 1:60". My favourite twist is the 1:72". This twist shoots well with several different cloth thicknesses and powder charges. The disadvantage, at least to some, is that you often have to use a heavy powder charge to achieve best possible accuracy. 1:66" is regarded by many as optimal.

The number of grooves is also a factor. Roundball barrels often have up to 8 grooves, while barrels intended to shoot conical bullets have fewer.

.50 calibre and conical bullet

With a conical bullet it is meant bullet types such as minié balls, maxi balls, Great Plains bullets, R.E.A.L. bullets or other long bullets. The rifling should be a bit shallower if you want to shoot conical bullets. .005" to .006" groove depth should be adequate. With such shallow rifling the grooves get a good grip of the lead and virtually screw the bullet out of the barrel. If the rifling is too deep the powder gases may blow by the bullet and ruin the accuracy.

1:24" to 1:28" twists should be optimal in a .50 calibre muzzleloading rifle and conical ball. If you use roundballs in such a slow twist you may experience serious accuracy problems, but you may want to try lower charges. These twist were actually quite common in large bore European Jaeger rifles in the 1700s, but the accuracy would probably have been better with slower twists.

.50 calibre and both roundball and conicals

Actually, most replica muzzleloading rifles being made today are made to shoot both roundballs and conical bullets. These rifles have what I call a compromise twist. Every compromise involves some give and take, and often the result is just halfway satisfying. This is my experience with compromise twists.

1:48" is a compromise which allows the shooter to use both roundball and conical bullets. If you want to shoot roundballs with a 1:48" twist you should try low charges, while conical bullets often require heavy loads. The Hawken brothers in St. Louis used the 1:48" twist in their rifles, so the twist is actually historically correct.

Recommended twists in a give calibre

Calibre	Roundball twist	Conical twist	Compromise
.36	1:48	1:16
.40	1:48	1:16, 1:18
.45	1:60, 1:66	1:18, 1:20	1:48
.50	1:66, 1:70, 1:72	1:24, 1:28	1:48
.54	1:70, 1:77	1:28, 1:32, 1:38	1:56
.58	1:70, 1:72, 1:83	1:32, 1:38, 1:48 *	1:60
.60

* = .58 calibre rifle muskets which were made to shoot minié balls often had 1:66", 1:72" or 1:78" twists. The reason is that the slow twist should reduce the horizontal drift on long ranges. Still, they are accurate with minié balls, but that they may be picky about powder charge. See the article about Rifle muskets and minié balls.