I took delivery of a custom .300 Winnie about 3 months ago and haven't had a good nights sleep since. It shot about any hand load around 1-1/4" (about what I expect for a new factory rifle, but $3500 should buy you much better). Yesterday, I tried a 200 gr Sierra GK over 63.6 gr of H 4831sc and viola, four consecutive shots into .488". A bit of experimentationwith seating depth ought to shrink that number a little-as would allowing the barrel to sufficeintly cool between shots. Velocity averaged 2612 fps for a ten-shot string- a bit ricey, but probably close to ideal for this non-premium bullet.

Is that load very far under max in the sierra manual? I have found that the SGK's I shoot in my .300 win like a load that isn't far above minimum.

This is a minimum load as listed by Sierra.

I have several reloading guides I use as references but my favorite is the Nosler 5th Edition for my 06's 300wm and other calibers. For 300wm 200gr nos pt, max charge 70.5gr of H4831 2910fps load density at 91% listed as the most accurate powder tested(use maximum loads with caution).I've found their load data for most accurate load tested is very accurate in my Sako Finnsport 300 win mag , my Sako 06 and Steyr Mannlicher Schoenauer 06.