Yes it does, but they did extensive tests using quite a few barrels with different groove configurations (depth, width, twist, etc.). With the musket, muzzle velocity is quite a bit lower than in a patched round ball gun. For the rifle-musket the average was 963 fps. In one test it was found that the faster the twist, the greater the "drift" of the bullet at longer ranges. Under a Table of Mean Drift I find the following:
The above is taken from the foregoing tables of co-ordinates of the centres of impact and with the exceptions notes, embraces all the shots fired in calm weather. From this it will be seen that the "drift", or tendency of the ball to deviate from the plane of fire, is in the direction of the twist of the grooves and increases with the inclination of the grooves and the distance passed over by the ball. It is not considered that the experiments were made under sufficiently favorable circumstances to enable us to verify with accuracy the laws which govern this peculiar deviation, but it is thought that they confirm the fact that a deviation, dependent on the normal rotation of the ball, does exist.
So the choice of a one in six twist was probably a compromise to achieve stability for the bullet and at the same time keep horizontal drift to a minimum. Different twists were experimented with, including a gain twist. The French, in their experiments figured that slowly increasing the twist from the breech to the muzzle would reduce the shock to the bullet as it expanded and started down the barrel. In the next paragraph, the writer admits that in practice he doubted that it would give the results that they expected. He said: "This may be owing to the change of form the ball must receive in it's passage through the bore, which change may increase it's liability to strip"
Both the Americans and French preferred to use an uneven number of grooves and I believe that the British came to the same conclusion. It appears that the bullet has to obdurate (spread) less to fill the grooves. Progressive depth rifling in experiments at Springfield resulted in less deviation and less drop to the bullet than a uniform depth rifling. The three broad, shallow grooves adopted in our musket were found to be easier to keep clean and cheaper to make, as well as less liable to damage from the head of the ramrod.
The final recommendation was that the grooves of all small arms be 3 in number, equal to the lands in width, rounded in shape; that the twist be a uniform spiral, one turn in six feet for the long, or musket barrels, and one turn in four feet for the short, or pistol barrels; and that the depths of all the grooves be cut uniformly decreasing, commencing in the musket at the breech with .015 inch, and ending at the muzzle with .005 inch; and in the pistol, at the breech with .008 inch, and ending at the muzzle with .005 inch; or, in other words, that the slope of the grooves of all small arms shall be the same, commencing at the muzzle with .005 inch in depth. (The above paragraph was taken from the report).
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