What are the advantages of having a bullet spin as it travels. I assume it is caused by the rifle, or groove on the inside of the barrel? Is it for accuracy?
Yes it is for accuracy, with early guns, you couldn't hit a barn door. The inside of the barrel has groves in a spiral pattern to spin the bullet, this greatly improves the accuracy.
Apparently an engineer by the name of Whitworth ( who is of screw thread fame ) came to the conclusion that one complete revolution per 20 inches of barrel length was the optimum figure.
During the Peninsula War 1812-1815 the majority of guns used were Muskets. Their accuracy was very poor since they were smooth bore. Some regiments used the Baker rifle, which as the name suggests had a rifled barrel, to increase accuracy and the term marksman/sharpshooter started to be used. I'm not 100% certain but I believe this was the first conflict that rifles were used in mass. To my knowledge the 60th and 95th Regiments used the Baker rifle.
Incidentally, the same principle is behind why the quarterback spins the ball when he makes a pass in American football. The ball will fly further, faster, and more accurately.
At the begining of all the James bond film's a man is seen walking in to the frame through the barrel of Bond's pistol , the 'twist's at the side's of the frame are I guess the grooves that make the bullet travel faster.
Not so much an answer but a bit more info. The man Whitworth actually made his slug with a twisted, hexagonal shape along its length. To accomodate this shaped slug he obviously had to have a twisted hexagonal hole up the barrel. Being mabe of lead the slugs deformed anough to make an air-tight seal along the barrel and the twisted hexagon of the barrel imparted the aforementioned spin. The man Whitworth was an absolute genius, he had hundreds of inventions. The army of course, never took up his idea for the hexagonal rifle which beat conventional rifles hands down in distance and accuracy. I thank you.
Does this mean that quarterbacks and rugby players have to alter the spin on the ball dependant on which hemisphere and the wind direction? So, if a soccer player or golfer in the southern hemisphere, playing between 35 and 45 degrees latitude, wanted his ball to curl left, which foot would he use? Would he strike the ball on the outside or inside or would he use his hand like Maradonna? I thank you.