This is what I found,don't know if it helps or not.
The .30-06 Springfield cartridge (pronounced "Thirty aught six") is a .308 inch (7.62 mm) caliber rifle cartridge, also known as the 7.62 x 63 mm, that was introduced as the standard cartridge of the United States Army in 1906.
It superseded the nearly identical .30-03 cartridge (introduced three years prior), but had a slightly shorter casing and a higher velocity spitzer bullet. The change to a pointed 'Spitzer' was in response to French and German developments during that time period. There were three main production runs of the round, that roughly correspond to large stocks built up during wars; the initial 30-06, the M1 ball and then the M2 ball.
The Springfield 1903 rifle, introduced alongside the earlier cartridge, was quickly modified to accept the .30-06. The .30-06 remained the US Army's main cartridge for nearly 50 years before it was finally replaced by the 7.62 x 51 mm with the official adoption of the M14 in 1954. However, the first M14s were not fielded until 1957, and the .30-06 remained in service into the 1970s, mainly as a machine gun cartridge.
It was used in the bolt-action M1903 Springfield and M1917 Enfield, the semi-automatic M1 Garand, the Browning Automatic Rifle (BAR), and numerous machineguns. It served the United States in both World Wars and in the Korea, serving as the basis for dozens of commercial and wildcat cartridges. Its last major use by the US military was in Vietnam. The .30-06's power, combined with the ready availability of surplus firearms chambered for it, has made it a popular hunting cartridge. It is suitable for hunting large mammals such as deer, elk, and moose.
30-06 and 30-06 SPR are the same cartridge. As Hammer1 said, it was developed by the Springfield Armory when they were a government owned arsenal. It's early civilian designation was typically G.I. 30 Gov. or some such, it is now standardized .30-06 Springfield as a civilian designation. The military has an official designator for it but commonly called it Cartridge Cal. 30 . It has remained the #1 selling big game hunting cartridge in N. America for decades.
Bring them in on a string. I love this term, if you want to be successful on calling in Elk, try not to just sound like the other caller. We all laugh at each other when we are practicing Elk calling at home or while camping. When I first started calling in Elk, I had no idea what i was doing and it's funny how many I could call in. The biggest Bull that I have called in to date was actually my first. I was making cow calls and screwing it up big time. But it's obvious I didn't screw up...