Must be the magnum barrel profile and the longer length, if indeed they use a heavier profile for the Saum like they do with the model 7.
I know on mine they said it was 5.5 lbs and it was no lie, I actually weighted it with a set of talleys on it and it weighted 5.5 lbs so naked it should be a hair less. The stocks are 24 oz FYI
Mine is getting hot rodded right now, I figured $1300 wasn't enough so I dedicded to drop another couple grand and soup it up a bit. It will be interesting to see if the weight will change much after its done.