It's a .30 caliber bullet. .30 caliber is the American designation for the size, 7.62 millimeters is the European designation.
Caliber should be on the barrel. SN's were not required until 1968
North American Arms
A large revolver
Depends on what caliber you are comparing it to.
American Heavy Machine Guns in WW2 fired .30 caliber rounds. The .50 caliber machine gun was 0.50 caliber which is 1/2-inch diameter and about 2 inches long. The shell before firing is about 6 inches in length.
No. But there WAS a submachinegun in caliber .22 Long rifle that fired 1200 rounds per minute, known as the American 180.
Probably late 1880's
10-100 USD or so
Blue Book of Gun Values
any sporting good store that sells ammunution................
You can try e-gunparts.com and gun shows.