01-28-2022, 06:47 PM
SCJim, the reamer print may not be terribly useful. You will be better off measuring with the bullets you will be using in your own barrel.
The reason for that is that the precise spot where the bullet touches the lands is largely affected by reamer wear. The spot where the lands begin to emerge is somewhere along the the 0.5 or 1.5 degree taper of the throat where a tiny bit of reamer wear (diameter change) moves the position back and forth quite a lot. Also, the exact spot on the BULLET where its curved ogive surface meets the land, which is itself at a shallow angle, depends on the ogive of that particular bullet. Secant ogives tend to be more sensitive than tangent ogives due to the geometry at the point where the shank ends and the ogive begins. That is partly why the "old faithful" bullet for the 6.5 Grendel is the 120 grain Matchking, since it tangent ogive makes it easier to tune.
The reason for that is that the precise spot where the bullet touches the lands is largely affected by reamer wear. The spot where the lands begin to emerge is somewhere along the the 0.5 or 1.5 degree taper of the throat where a tiny bit of reamer wear (diameter change) moves the position back and forth quite a lot. Also, the exact spot on the BULLET where its curved ogive surface meets the land, which is itself at a shallow angle, depends on the ogive of that particular bullet. Secant ogives tend to be more sensitive than tangent ogives due to the geometry at the point where the shank ends and the ogive begins. That is partly why the "old faithful" bullet for the 6.5 Grendel is the 120 grain Matchking, since it tangent ogive makes it easier to tune.