There is no difference at all between the names you see today printed on the boxes. The full name is the 30-06 springfield which is 30 caliber made in 1906 by Springfield. However it is just common today to call it the 30-06. The other is probably 30-06 SPRG. which is just an abreviation. They are all the exact same cartridge.



Here is a gool little read about the 30-06 and the springfield rifle.
http://www.france-collection.com/1903/accueil1903.htm

The round was originally the 30-03 springfield because it was developed in 1903 for the Springfield 03 rifle. 30 caliber made in or model 1903

In 1906 the cartridge was modified slightly and became known as the 30-06 springfield. 30 caliber made in or model 1906. It was also chambered in the springfield 03 rifle. Although the rifles had to be modified to shoot the new 30-06 cartridge.