We've made up a max COL measuring tool. As a staring point we used the Frankford Arsenal tool, but improved it ( at least that is my idea). I shoot 243 with 75 grain HDY and 67 grain Hornady bullets. This only on the range for practice. My first load was about 0,8 mm ( 0,032 " ) of the grooves and lands. Accuracy was reasonable, but not perfect. I could shoot a few 14mm, 3 shot groups at 100m , but also groups wich are 40mm / 50 mm .
After measuring the max COL we ( my reloading friend and myself) made up the same load but with 0,5 mm of jump. ( about 0,02") and the groups get worse. Checked the loads in the rifle , no marks on the bullets when chambered, no overpressure signs,...... As a starting reloader I have no idea what can be the reason?
load : 243 win , 75 gr HDY , 44.4 grain Ramshot Hunter - Rifle : Rem 700
The first load ( 0,8 mm off ) was made up along a reloading book, never measured anything.
The new loads I tried with the 87 grain bullet and also 0,5 mm jump also have bad accuracy.