The .338 Remington Ultra Magnum is a .338 caliber rifle

Rifle

A rifle is a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the projectile , imparting spin around an axis corresponding to the...

 cartridge

Cartridge (firearms)

A cartridge, also called a round, packages the bullet, gunpowder and primer into a single metallic case precisely made to fit the firing chamber of a firearm. The primer is a small charge of impact-sensitive chemical that may be located at the center of the case head or at its rim . Electrically...

 introduced by Remington Arms

Remington Arms

Remington Arms Company, Inc. was founded in 1816 by Eliphalet Remington in Ilion, New York, as E. Remington and Sons. It is the oldest company in the United States which still makes its original product, and is the oldest continuously operating manufacturer in North America. It is the only U.S....

 in 2002. It is a beltless, rebated rim cartridge based on the .300 Remington Ultra Magnum

.300 Remington Ultra Magnum

The .300 Remington Ultra Magnum, also known as the .300 Ultra Mag or .300 RUM is a 7.62 mm caliber rifle cartridge , 7.62x72mm, or .30 caliber rifle cartridge introduced by Remington Arms in 1999. The .300 Remington Ultra Magnum is one of the largest commercially available .30 caliber magnums...

 case shortened .090" loaded with a .338 caliber bullet. The .338 Remington Ultra Magnum is second only to the .338 Lapua Magnum and .338-378 Weatherby Magnum

.338-378 Weatherby Magnum

The .338-378 Weatherby Magnum started out as the wildcat cartridge, .338-378 Keith-Thomson Magnum during the early 1960s. Keith and Thomson are Elmer Keith and R.W. "Bob" Thomson. The 338-378 Keith-Thomson Magnum is slightly shorter than the .338-378 Weatherby Magnum. However this is only a neck...

 in cartridge-case capacity.

Because this cartridge already operates at very high pressures (65,000 PSI), Handloaders

Handloading

Handloading or reloading is the process of loading firearm cartridges or shotgun shells by assembling the individual components , rather than purchasing completely assembled, factory-loaded cartridges...

cannot give significant improvements over factory ammunition as many handloaders have done over the years with more conventional, lower pressure rounds.