I mesured some factory 300wsm ammo Win surpreme 180 BT and got 2.823...
then I mesured a Fed prem 300wsm 180 gr accu bond and got 2.820...

I mesaured my COL using the split case method and I'm coming up with COL of 2.957 to 2.959... Does this seem a little to long???

Magnums have some long throats. Just the way it is. It to keep that initial pressure spike down. You think that is bad, my 300RUM had 3.82" with 180gr barnes bullets to the rifling. But its hard to find a bullet you can load that long and factory data was normally 3.58".

You'll find much shorter throats in your 308's and 30-06s. The most important thing is your not in the rifling and you can fit the loaded round in your mag.

BC,

I was measuring my accubonds the other day and came up with the exact same distance to the lands. What did you end up using as a COL for your loads?

For my 300RUM, with a 700 action, longest I could go is 3.625" and fit in mag with some room. So I went with 3.62" on average.