Lapua's website has the story of the genesis of the .338 Lapua Magnum cartridge, and it is an interesting read.
The birth of the .338 Lapua Magnum dates back to 1982, when an American company Research Armament Industries, RAI (Rogers, Arkansas) was asked by the United States Marine forces to develop a long-range rifle for sniper applications. RAI was a relatively small company, owned by late Jerry Haskins, operating mainly in the field of defense technology projects. Officially the project was to develop a target rifle for 1000 yards, but in reality the purpose was more likely to develop a 1500 m sniper rifle.
The primary rifle manufacturer ended up to be Accuracy International, owned by Malcolm Cooper in Great Britain.
The Accuracy International rifle became the first mass production .338 Lapua Magnum rifle.
Among the wildcat versions of the .338 Lapua Magnum, the 6.5-338 Lapua remains possible the as the fastest. Originally designed in Finland, it has to be one of the highest velocity cartridges in this bore size.
Here is a link to the entire story, and holy heck batman would a 6.5-338 be smoking...