By which side? The US and its allies used 7.62x51 for their sniper rifles. The North Vietnamese typically used 7.62x54R for theirs.
In California.
22 LR up to and beyond 50 BMG
You will have to define the term "Sniper rifle". It could mean anything. The only TRUE sniper rifle is a rifle issued to a sniper. They are simply rifles that are capable of long range accurate shooting. The rifles used by US military snipers during the Vietnam was were simply civilian hunting rifles with decent telescopes.
Yes. You can get replacement springs for airsoft sniper rifles.
The manufacturer is spelled Barrett (Barrett Firearms Manufacturing), builder of the M82 and XM500 .50 caliber sniper rifles that fire the 12.7x99mm NATO round (Browning machine gun round).
It is often accepted the Heckler and Koch PSG-1 is the most accurate sniper rifle in the world.
USMC Gunnery SGT. Carlos Hathcock had a documented over 60 confirmed kills. But he used a standard bolt action hunting rifle, which used standard center fire hunting cartridges (30 caliber category). All medium hunting calibers were thirty caliber which included 7mm, 8mm, .303, 7.7, 308 (7.62mm), 30-06, 30-30, 30-40, etc. Varmit cartridges used to be the .22 range such as the 218 Bee, 219 Zipper, 221 Fireball, 222 Remington, 223 (M16 Jungle Rifle/5.56mm), etc. The Viet War didn't have computerized sniper rifles, Laser Range Finders, and other bells and whistles. Nor did it have .50 BMG (Browning Machine Gun) sniper rifles. When Gunny made his .50 kill it was with the standard issue fifty caliber machine gun set on single fire. And one more item, Vietnam and WWII snipers HUNTED men; which required CARRYING their rifle over mountains and through swamps for days and days. No sniper could carry today's super heavy .50 caliber BMG special sniper rifles with their accompanying scopes, bi-pods, tri-pods, and electronic/computer devices by themselves over mountains, hills, swamps, and through jungles. Todays super dooper sniper rifles are "precision shooting instruments" designed for precision shooting at extremely long ranges; Vietnam was about killing and the standard hunting rifle did the trick.
Sniper rifles are just high caliber rifles fitted with a scope, if you are looking for a legal civilian good bolt action rifle i would stick with an m40a1, Remington 700, or M24, these rifles range from about 2,500$-10,000$+. If you want a nice semi auto stick with something like a psg1 or m110, m21's are good too, these rifles are usually 5,500$+ and chamberd for a 7.62x39mm round.
Also known as 7.62 NATO, this was the standard full powered rifle caliber for all NATO nations. Rifles included the M14, the British L1A1, the Belgian FN FAL, and even India had a bolt action version of the Enfield in that caliber. It is also used in the M60 machinegun, various sniper rifles, etc.
Paintball sniper rifles are sold anywhere ammunition and gun supplies are sold. Walmart carries paintball rifles and accessories as well in most of their stores.
The .45 caliber bullet is not used in a sniper rifle.
Local stores that sell guns or weapons will have a variety of information for an consumer with questions about sniper rifles. Academy and Wal-Mart are two different providers of guns and weapons who also sell sniper rifles.