It's a good caliber, yes.
Short answer is Remington. But it is a mix of parts. The action is that of a Remington 700. http://en.wikipedia.org/wiki/M24_Sniper_Weapon_System The above is the Army sniper rifle. Gibbs used the Marine m40. In the episode you're referring to, the rifle Ari used was a Bravo 51, chambered in .308 Lapua. This rifle doesn't exist. There is a Bravo 51, but it is chambered in .338 Lapua. There is no .308 Lapua. The Bravo 51 is named "Kate" and the rifle is only available in .338 Lapua. This platform is available in other calibers, but have different names. The TV show mixed stuff, but it's just a show.
See related links below Clarification: 7.62x51mm, .300 Winchester Magnum, and .338 Lapua Magnum are the most popular.
The ".338 Lapua Magnum" is a rimless bottleneck shaped cartridge that is designed for use in long range sniper rifles. It was released in 1989 and is still in use today.
L115A3, otherwise known as the Accuracy International Arctic Warfare. It fires the 8.58x70 cartridge (also known as .338 Lapua Magnum), and the shots made actually exceeded the projected range of the rifle.
Your question is a bit ambiguous, so I'll go with the notion you're referring to the longest confirmed kill by a sniper. That was achieved with a rifle chambered in .338 Lapua Magnum.
No, it is a .338.
We'll, a Canadian sniper pulled off a kill at more than 1.5 miles
There is no .338 Lapua Super Magnum. There is a .338 Lapua Magnum which is considered a member of "Super Magnum family". .338 LM uses several different bullet types and drop will depend on bullet type and weight.
Depends on the rifle. A .22 is accurate to about 100 yards, can fire a bullet about 1.5 miles. A .338 Lapua is accurate to about 1500 yards, and can fire a bullet ABOUT 5 miles.
It depends on the rifle. The .300 Winchester Magnum has a muzzle velocity in excess of 3000 feet per second (914 meters/sec). The .338 Lapua Magnum runs about 823 m/s (2,700 ft/s). The .50 Browning is in the same general range. All are handloaded for sniper use, so details may vary with the bullet weight and adjustments made for the particular rifle and scope.
Each will perform as intended within its range limitations.
375,000 yards