Working up loads for my new 300 win mag. (Will post pictures soon) Using a hornady overall length gauge and comparator with a hornady modified 300 win mag casing I am measuring the length to lands with a 230 berger hybrid bullet. I am consistently coming up with 2.902" from base to ogive. But my question is, after I fire a case in my chamber it reads 2.270" from base to datum of shoulder and I bump that back to 2.269". On this hornady modified case from base to shoulder measures 2.258" meaning it is .011" shorter than what I will be actually firing. I know the best way to solve this problem would be to modify a once fired casing but until I do this what do I seat my bullets to for touching the lands? I have been crunching numbers and running scenarios on this for a while now and still cant figure it out. Also because I am headspacing my brass off the shoulder not the belt, is this why it is so far off? And even if so, how do you account for this? What I'm trying to figure out is do I add .011" to my 2.902" meaning on a properly sized case touching the lands would be 2.913" or is this not right because something to do with the belt coming into contact before the .011" longer shoulder would?