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tlturbo · 11-09-2007, 17:10 PM

I've never seen the band itself called a cannalure. We have always called it a driving band (because it and the rifling drive the projectile around) but I guess I've never really seen it named that. It's always called a rotating band like Rusty said. But a cannalure is a groove or group of grooves. On a small arms bullet (if necessary) it is a ring of little notches located where the top of the case would be on a loaded round and allows a slight crimp in the neck lip of the case to be pressed into the bullet to help hold it in the case. In a large projectile, like a 16", it is the several groves that go around the rotating band to allow copper that is displaced rearward by the rifling to accumulate. Like stated before, the bourrelet isn't a groove but an oversized portion of the projectile that rides on the top of the lands.

Here is an excerpt from Slovers site.

3D3. The bourrelet

The forward bearing surface of a projectile is machined to a fine finish to reduce friction and minimize the wear of the gun. In small projectiles the entire body forward of the rotating band may be finished to bourrelet diameter. On large-caliber projectiles additional bourrelets, abaft and forward of the rotating band, are added to provide better support, especially during ejection from the muzzle. A certain clearance must be provided between the bourrelet and the lands (the raised portions of the rifling). Standard United States Navy practice requires a specified bourrelet diameter 0.015 to 0.023 inch (in different-caliber projectiles) smaller than the diameter of the bore. To this margin is added a manufacturing tolerance of minus 0.005 to 0.007 inch, so that total clearance limits vary from 0.015 to 0.030 inch. Unnecessary clearance adversely affects accuracy and fuze performance and may mar the rifling by excessive wobble.

3D4. Rotating band

The three primary functions of the rotating band are to seal the bore, to position and center the rear end of the projectile, and to impart rotation to the projectile. Its secondary function is to hold the projectile in its proper position in the gun after loading and ramming, and to ensure that it will not slip back when the gun is elevated. The band has considerable effect on muzzle velocity, range, accuracy, and the life of the gun.

Rotating bands are usually made of fine copper; in major-caliber projectiles a small percentage of nickel is added to provide greater strength. Some projectiles of recent design have been banded with gilding metal (90 percent copper, 10 percent zinc), which increases strength and reduces the amount of copper deposited in the bore of the gun.

To reduce dependency on copper for this use (copper is increasing in military importance while it becomes scarcer and more expensive) rotating bands of sintered iron are under development.

United States Navy projectiles generally have rotating bands about one-third caliber in width. Foreign services sometimes use narrow multiple bands on major-caliber projectiles. The rough band is assembled (after heating it, in 8-inch and larger calibers) by slipping it over the rear of the projectile and pressing it into a score cut into the body of the projectile. This scoring usually includes a dovetail on each edge to assure that the band will not be thrown off by centrifugal force. Either waved ridges, longitudinal nicks, or knurling are provided on the bottom of the score to ensure against band slippage during rotary acceleration.

The forward edge of the band is slightly conical, to facilitate engagement with the origin of rifling. The cone, during loading, wedges into a seat at the origin of the rifling (except in fixed ammunition) and holds the projectile in place during loading and elevating. The central portion of the band is cylindrical and of a slightly greater diameter than that of the bore plus the depth of the rifling. This portion is sometimes divided by circumferential grooves, called cannelures, which provide space into which displaced copper may be wiped. In the after part of the band separate-loading projectiles have a raised lip followed by an especially deep cannelure. The lip serves to ensure a good gas check and also to prevent overramming in a badly worn or eroded gun.

The purpose of the cannelures is to minimize the formation of a fringe or skirt from the excess metal which is wiped rearward. Such a fringe is likely to flare outward, at the muzzle of the gun, due to the effects of the gases and of centrifugal force, and cause loss of range and accuracy. Bands on which the lip is well forward of the end of the band and is undercut with a deep cannelure are known as nonfringing.

11-09-2007, 17:10 PM	#22 (permalink)
tlturbo Regular Join Date: 01-26-07 Location: Lake Worth, FL Posts: 48	I've never seen the band itself called a cannalure. We have always called it a driving band (because it and the rifling drive the projectile around) but I guess I've never really seen it named that. It's always called a rotating band like Rusty said. But a cannalure is a groove or group of grooves. On a small arms bullet (if necessary) it is a ring of little notches located where the top of the case would be on a loaded round and allows a slight crimp in the neck lip of the case to be pressed into the bullet to help hold it in the case. In a large projectile, like a 16", it is the several groves that go around the rotating band to allow copper that is displaced rearward by the rifling to accumulate. Like stated before, the bourrelet isn't a groove but an oversized portion of the projectile that rides on the top of the lands. Here is an excerpt from Slovers site. 3D3. The bourrelet The forward bearing surface of a projectile is machined to a fine finish to reduce friction and minimize the wear of the gun. In small projectiles the entire body forward of the rotating band may be finished to bourrelet diameter. On large-caliber projectiles additional bourrelets, abaft and forward of the rotating band, are added to provide better support, especially during ejection from the muzzle. A certain clearance must be provided between the bourrelet and the lands (the raised portions of the rifling). Standard United States Navy practice requires a specified bourrelet diameter 0.015 to 0.023 inch (in different-caliber projectiles) smaller than the diameter of the bore. To this margin is added a manufacturing tolerance of minus 0.005 to 0.007 inch, so that total clearance limits vary from 0.015 to 0.030 inch. Unnecessary clearance adversely affects accuracy and fuze performance and may mar the rifling by excessive wobble. 3D4. Rotating band The three primary functions of the rotating band are to seal the bore, to position and center the rear end of the projectile, and to impart rotation to the projectile. Its secondary function is to hold the projectile in its proper position in the gun after loading and ramming, and to ensure that it will not slip back when the gun is elevated. The band has considerable effect on muzzle velocity, range, accuracy, and the life of the gun. Rotating bands are usually made of fine copper; in major-caliber projectiles a small percentage of nickel is added to provide greater strength. Some projectiles of recent design have been banded with gilding metal (90 percent copper, 10 percent zinc), which increases strength and reduces the amount of copper deposited in the bore of the gun. To reduce dependency on copper for this use (copper is increasing in military importance while it becomes scarcer and more expensive) rotating bands of sintered iron are under development. United States Navy projectiles generally have rotating bands about one-third caliber in width. Foreign services sometimes use narrow multiple bands on major-caliber projectiles. The rough band is assembled (after heating it, in 8-inch and larger calibers) by slipping it over the rear of the projectile and pressing it into a score cut into the body of the projectile. This scoring usually includes a dovetail on each edge to assure that the band will not be thrown off by centrifugal force. Either waved ridges, longitudinal nicks, or knurling are provided on the bottom of the score to ensure against band slippage during rotary acceleration. The forward edge of the band is slightly conical, to facilitate engagement with the origin of rifling. The cone, during loading, wedges into a seat at the origin of the rifling (except in fixed ammunition) and holds the projectile in place during loading and elevating. The central portion of the band is cylindrical and of a slightly greater diameter than that of the bore plus the depth of the rifling. This portion is sometimes divided by circumferential grooves, called cannelures, which provide space into which displaced copper may be wiped. In the after part of the band separate-loading projectiles have a raised lip followed by an especially deep cannelure. The lip serves to ensure a good gas check and also to prevent overramming in a badly worn or eroded gun. The purpose of the cannelures is to minimize the formation of a fringe or skirt from the excess metal which is wiped rearward. Such a fringe is likely to flare outward, at the muzzle of the gun, due to the effects of the gases and of centrifugal force, and cause loss of range and accuracy. Bands on which the lip is well forward of the end of the band and is undercut with a deep cannelure are known as nonfringing.