You stated the COAL is well below magazine COAL. Factory round did same. That points to throat for me.
1-scope the throat to see if there is anything there to interfere with bullet. Anything from lint, brass, carbon etc can cause this.
2-have you actually measured the max CBTO and max COAL with a comparator instead of using magazine as COAL reference?
3-Sharpie the heck out of bullet ogive and see if there are any rub marks.
Good luck!
1-scope the throat to see if there is anything there to interfere with bullet. Anything from lint, brass, carbon etc can cause this.
2-have you actually measured the max CBTO and max COAL with a comparator instead of using magazine as COAL reference?
3-Sharpie the heck out of bullet ogive and see if there are any rub marks.
Good luck!