Good morning from the Verde River,
Some questions on rifling twist (in rifles, not pistols or revolvers). Right or wrong, in the past the extent of my knowledge regarding rifling twists was:
- 1:66/1:56 were slow twists and best for patched round ball.
- 1:48 was an all-purpose faster twist which shot both round balls and conicals effectively.
- 1:32/1:28 and lower were very fast twists used for sabots.
So slower twists are found in some original hunting rifles for round ball, and even in some military rifles for conical Minnie Ball. Part of the equation is the depth and width of the rifling. Some original rifling grooves we'd call "thin" in width, compared to modern rifling. The rifles that benefit from very slow twists often used whopping huge powder loads with patched round balls.
Then you also have the "gain twist" barrels which finish giving the patched round ball a twist of 1:48 or sometimes faster.
1:48 was a super common twist rate before conical bullets started to be commonly found. It was in the 1970's that manufacturers found that it also worked for both conicals and round ball, so they marketed them that way ...,
a compromise ; good for both...
Faster twist rates were well known in Germany during the 18th and 19th century, BUT these were on a lot of target rifles, and a fast twist rate might cause, as the British documented in a manual in 1802...,
a disagreeable recoil... (Likey due to torque from the stock against the shooter's cheek)
On looking at past posts I am seeing that it isn’t as simple as that, there are more variables involved. So, I have some questions.
- Does barrel length affect the accuracy more so in a slower or faster twist?
- Does the 1:66 twist require a larger load for effective accuracy?
- If you had 2 barrels in the same caliber and length; one a 1:28 and the other a 1:48 twist, would the 1:48 require a larger charge for effective accuracy?
- If you had 2 barrels in the same caliber and twist; one 28” long and one 36” long, would they both require the same charge for effective accuracy?
So for the spin to give your round ball an advantage, the ball needs to turn 1/4 of a revolution before exiting the barrel. This was discovered by the British when designing the Baker rifle. After that, it's all good. Conical bullets are a different matter.
The twists slower than a 1:48 allow for a really large charge, but since we're not using hand rifled barrels, the rifling of a 1:48 twist will handle some pretty good loads. Now if you are James Forsyth in 1867, trying to drop a rhino with a 4 bore launching a ball that weighs about 4 ounces.., you will likely want that 1:108 - 1:120 twist rate barrel and be shooting 250 grains of powder.
question 1
Barrel length doesn't really effect accuracy in two loads going exactly the same muzzle velocity. Accuracy is then more of a function of consistent MV, and how well the shooter's eyesight interacts with the sights. Normally, the farther apart the front and rear sight..., the easier it is for a human eye to judge an accurate shot. This is called the "sight plane".
question 2
Nope, the 1:66 twist rate does not need a heavy load when using a round ball, BUT you might find it does not stabilize a conical well depending on how the rifling was cut and the design of the bullet. Some folks that report that their "slow twist" barrel seems to work better with a conical when a heavy charge is used are actually getting "better" results because of the quicker flight time to the target = less error by a not fully stable bullet. Sometimes this also applies to round ball for the same reason... faster flight = less error at the target...
question 3
Nope, the spin rate isn't doing anything for you after the bullet is stabilized. It's not like a modern, jacketed bullet.
question 4
Again, the effective accuracy is going to be more from your eye interaction with the sights, than the load, although the lighter the load, the greater the flight time to the target, and thus the more that gravity will act on the ball, and the more time for a cross wind to push on the ball. So your eye may be able to be more precise when lining up the sights on the target with the longer barrel.
Now coupled with that..., how consistent is the load from shot to shot, and how consistent the muzzle velocity ??? Meaning..., you have well made barrel, a good set of sights, and you can see them well. Your rifle action is fast as well. So then..., when you measure out the powder, how consistent is your method from shot to shot? Is it good? OK great..., then..., how well is your patched bullet sealed, and are you getting very close to the same muzzle velocity for each shot?
Consistency is the key. It was 250 years ago, and is today, even in modern stuff. The farther away the target, the more the inconsistency shows up on the target. My son can reach out 1000 yards using something modern, not because he has a special twist rater compared to the next guy who doesn't hit much of anything..., but because my son has developed nearly identical loads for his modern stuff. I can get some amazing accuracy from my balck powder 1:48 twist rifle as well as my 1:56 twist rate rifle..., when I'm very careful about my loads, and especially from the bench with the rifle pretty much locked into the same position for every shot.... which = very similar shooting conditions.
..., put me behind the sight, holding the rifle on top of the bench instead of using a rest and sandbags etc..., the results on the target change showing less accuracy...
You will have happy results with a .440 ball out to 75 yards and likely out to 100
You can get the same results or maybe even better with a .350 ball BUT the wind will not be your "friend"
A .390 ball will give you a lighter recoil with an identical load to the .440, and they are often used by target shooters, and "buck the wind" better than the .350... but not as well as a .440.
LD
