COL

I just started reloading my 7mm rem mag.
I determined the COL by starting with an umprimed case and bullet set to just seat. I then tried this in my gun until the bolt would close.
Then I put dry erase marker on the bullet and the loked for marks showing I was contacting the lands. It was.
The COL was 0.100 inch longer than the Hornady manual has for the bullet. The Hodgdon manual was also shorter.
Does this happen? Have I mismeasured somehow?
My 243 was shorter than the Hornady COL making the 7mm a surprise when it was longer.

Every rifle will be different. They give a suggested COL that should work in just about anything.Welcome to the world of unlimited variables.

those books show the col that they tested and FPS they got useing that data, what you did is went to lands none of the data in any book will have you at the lands, usually most start some where near what that data book says for col then move closer to lands to fine tune their load, you did what I do , I start at lands and work with my powder for best accuracy if that doesnt work I go a .005 jump from lands and try again untill I find the sweet spot that most barrels have , where your accuracy is the best.

+1 on starting at the lands. I always start load production at the lands. Thats where the highest pressure would show. After I find the load I like then i play with seating depth to fine tune. After that then on to action screws for final fine tuning.

As said, nothing is etched in stone.... Except death.

IME, MOST bullets will shoot decently when seated about 1/16th shorter than the lands. I use the same method to determine OAL for any given bullet.