Can anyone tell me the difference between the 6.5 SAUM and the 6.5-300 REM. SAUM?
Thanks,
Terry

You can buy 6.5 SAUM brass, would be one thing.

http://www.gaprecision.net/ga-store/brass.html

They are the same to my knowledge. The "300 SAUM" just describes the parent case as opposed to 300 WSM.

The 6.5 SAUM brass fits nicely in my 6.5-300saum rifle.

They are the same thing. 7saum or 300saum necked down is all.

The necks are turned on the 6.5 saum do they do the same on the 6.5-300 saum?

Depends on the neck diameter of your chamber, no other reason.