Yet another load work-up question:
Shooting strings of 6 shots each with 55.0 and 55.5 grains of powder, I get 2 rounds in each string that chronograph roughly 400 fps below the other four in the string.
I do not have this problem with other shot strings, from the starting load up to and including 54.5 grains. I do not have this problem with strings loaded with 56.0 or 56.5 grains.
Groups with the two weird strings (55.0 and 55.5) are roughly 3/4 inch larger than groups with lower and higher charges.
What in Heaven is going on here? Bad chronograph? Funky primers? My rifle hates the number 55?
For all loads:
Win nickle brass - all from Winchester factory ammo, all fired one time through the same rifle used to work up this load. All cases neck-sized with the same die - no adjustments. All deburred and chamfered with the same tool. All brass trimmed to the same length.
All primed with WLR primers from the same box, seated with the same press.
All charged with IMR 4350 from the same canister. All charges thrown and then weighed on the same balance, on a wooden surface, without moving or adjusting it. After each charge weight is loaded, the balance is checked for zero, then set to the next charge weight.
All loaded with 180-grain bullets from the same box.
The barrel is allowed to cool after every shot. The barrel is cleaned betweeen each string.
I'm pulling my hair out trying to figure out why there are 4 rounds on my chronograph that don't make any apparent sense. Can anyone explain this to me?