Some law enforcement agencies have used the .270 as a sharpshooter's weapon, but it was never military issue.
The .45 caliber bullet is not used in a sniper rifle.
Navy SEAL snipers used the .30-06 caliber M40A5 sniper rifle to free Captain Phillips of the Maersk Alabama.
Assuming you're referring to the M1903A6, it used the 7.62x63mm cartridge, more popularly known as the .30-06.
Any bullet that has a diameter of one half inch is a .50 caliber bullet. There are different .50 caliber bullets- my Hawken muzzle loading rifle shoots a .50 caliber lead bullet, but different from the .50 Browning Machine Gun (that is also used in the .50 Barret sniper rifle)
A sniper rifle is a precision rifle that has a telescopic sight which allows operators to target an object that is far in the distance. Sniper rifles are used in military combat.
In the case of the Barrett M82 rifle, about 30-31 lbs, depending on the model. The scope may add several more pounds if a night vision scope is used.
If you mean the SVD Sniper rifle manufactured by the Soviet Union, no, it is not a .50 caliber weapon. It fires a match grade version of the 7.62 X 54R cartridge- the same round used by the Moisin-Nagant 91/30 rifle (and the M38 and M44 Carbines). Wikipedia has a good concise article on the Dragunov sniper rifle. Enjoy.
WWII
A sniper rifle used in ww2.
The PTRS is mainly used as an anti- tank sniper and the 50 cal is just a normal sniper rifle. =============== The PTRS was a sniper rifle made by the Russians during world war 2, it was used to take down heavy infantry and light vehicles like half tracks and jeeps. The Barret 50 Calibre sniper rifle is an anti-infantry sniper rifle, used for all purpose battlefield deployment. However, the modern day anti-armour sniper is the Intervention, this bolt-action sniper rifle is used in Call Of Duty Modern Warfare 2 (wow... took me ages to write that title) which for some reason does no more damage than the Barret. The intervention can slice through light-to-medium armour in seconds, killing anybody inside.
A sniper rifle is simply a rifle used by a military sniper. Just about every gun shop will carry hunting rifles. The type will vary depending on what you are hunting- squirrels, rabbit, deer, turkey, bear, elk or elephants. What you are calling a "sniper rifle" is simply a bolt action center fire rifle with a telescope.
By which side? The US and its allies used 7.62x51 for their sniper rifles. The North Vietnamese typically used 7.62x54R for theirs.