If you mean the .50 BMG (there ARE other .50 caliber cartridges) it is a restricted firearm, requires licensing. There was a move to ban further imports of .50 cal BMG AMMO and rifles, but do not know where that stands.
Depends on where you live, and WHICH .50 cal. California has banned rifles that fire the .50 Browning Machine Gun cartridge. Other state have not. Please note there are several .50 cal firearms- including .50 caliber muzzleloading black powder rifles.
Air Rifles come in several different bores. .177, .20, .22, .25, 9mm, 45 Cal, 357, and 50 Cal. Big bore usually refers to the 9mm, 45 Cal and 50 Cal. These rifles fall into the PCP class of Air Rifles.
50 and up
Yes
4/100's of an inch. .50 cal = .5 inch .54 cal = .54 inch
no, 50. cal are illegal in australia, but theres some similar legal calibers, like the 460.
Barrett makes a range of .50 rifles, some of which are self loading (semiautomatic), and some of which are bolt action. The most famous of these rifles is the M92/M107, which is semiautomatic.
It depends on what state you live in.
Intervention Barrett 50 cal. WA2000 M12 EBR
Large bore muzzleloading rifles (.50 cal and larger) and muzzleloading shotguns.
Sure. I like pictures of Hawken rifles.