Re: 30 / 8mm Rem Mag
The 30/8mm is also known as the "308 Super".
It's the 8mm Mag necked down to 308 diameter.
Had one or two of these chamberings years ago for the 1000 yard matches at Williamsport.
It's a good cartridge but, most people like the 35 degree shoulder on the 308 Baer or 308 Goodling cartridges better then the 25 degree on the 308 Super.
Both cartridges mentioned above were made from the 300 Weatherby cases.
The 7mm STW is made from the 8mm Mag case with no other change other then necking down to 284" diameter.