November 4, 2008, 12:32 AM
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#2
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Senior Member
Join Date: November 3, 2002
Posts: 251
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Here is what Wikipedia has to say on the subject (with my comments in Italics):
The defining characteristic of the Foster slug is the deep hollow in the rear, which places the center of mass very near the tip of the slug, much like a shuttlecock. If the slug begins to tumble in flight, drag will tend to push the slug back into straight flight. This gives the Foster slug stability and allows for accurate shooting out to ranges of about 75 yards (about 70 meters). Most Foster slugs also have "rifling", which consists of thin fins on the outside of the slug. Contrary to popular belief, these fins actually impart no spin onto the slug as it travels through the air. Since the slug is fired at a supersonic velocity, the nose of the slug pushing a shockwave creates a vacuum on the side of the slug, where the fins are located [and thus no aerodynamic effect from the fins since there is no (or little) air around the fins, at least while traveling at supersonic speeds]. The actual purpose of the fins is to allow the slug to safely be swaged down when fired through a choke [and thus be centered in the barrel throughout its travel through the bore], although accuracy will suffer when such a slug is fired through tighter chokes. What I've read elsewhere is to similar effect.
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