I have a Accumark .30-378 Wby; I use 180 grs bullets,Nosler BST,Barnes X,Speer SBT.Powders H-4831sc,H-1000;H-870.Full length sizing or neck sizing.Rcbs dies used,I have played with the deep of the sizer and with the neck tension of the neck sizer; the problem is I cannot group less than two inches at 100 yards;should I go with lighter bullets as 165 grs;150 grs. I dont plan to go with heavier bullets, it will be I think worse...

I don't own a 30-378 but I do own a lot of wbys. Try to shoot a flat base bullet if you haven't. I have noticed wby's seem to like these better then boattails.

As dumb as it sounds, it seems to be true.

If the gun does not hold better then 1.5 moa send it back and they will make it work. They are pretty good about that stuff.

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My sako tgrs didn't like heavy bullets. It seems to like the 150's and down. (It really loves 125 nosler ballistic tips--there's a great hunting combo!) I finally settled on 150 barnes xbt's. It shoots them to about 4" at 300 yds. Good luck--I wish the RUM was out at the same time--I wouldn't own a 30-378 now. My gunsmith says he hears lots of stories of bad accuracy near max. If you want to slow it down to 300 wby and under I'll bet it will shoot! (sorry not to make your day!)

Don Krakenberger; .300 RUM instead of the .30-378 Wby I agree.The .30-378 Wby with 150 grs bullets or lighter seems the way to go. I will try 150 grs Barnes X;and bullets between 125-150 grs. I think with this rifle someone has to generate very high velocity,near 3500 fps.