Two weeks ago I tested a batch of hand loads in a 270, using 59.5gr of 4831sc and varying the jump. At 0.1, 0.3, and 0.4" groups were sub-moa, with 0.4 being the best (0.7 moa) Fast forward two weeks. I neck sized the brass from the last session and loaded about 20 to mimic that best group, with 0.4" jump. Those rounds loaded to jump 0.4 were well over an inch, at the next range visit.
I feel like the shooter and gun were proven with the first session. What direction would you go to figure this out?
What kind of rifle, and has it been tuned up re trigger and bedding?
You say you neck sized the brass for the newer batch. Was the first batch neck sized? Also, what kind of die did you use to neck size? The "regular" type neck sizers don't always produce the straightest sized brass.
Do you know the runout of the assembled cartridges for both batches?
When the first batch was "proven," how many shots were in the groups, and how many groups did you shoot? Small sample sizes don't prove much.
