I'd be grateful for help diagnosing a niggling accuracy problem:
I have a recently acquired .308, with a 6X42 scope in swing off mounts. For the purposes of this, it was being shot off a bipod.
After trialling a few different factory loads, I decided on Norma 150gr ballistic tips. These consistently produced goups under an inch at 100 yards at the first range session.
Yesterday I did some more range work, and was unable to replicate this, ending up with an average group of around 2.5 inches.
However, there was a distinct pattern to the shots: the first in each subsequent group of three went almost through the same hole (ie. if I were to only take those shots, there would be a very nice group indeed). The second went about half an inch high and a touch to the left, but with more variability, and the third about an inch and a half high with a lot of variability.
Since I zero using a new post it note stuck on top of the last after each group, at the end of the session, I can peel them all away and look at the aggregate group on the cardboard underneath. This showed 3 distinct groups for each shot.
Nothing had changed with the rifle in between the two sessions, and it had not received any knocks - I am confident that there is nothing wrong with the set up.
So my question is this: is such a pattern likely to be the product of something shifting as the barrel heats up with each successive shot in a group? Or can it be explained by my tendency to develop a flinch?
I am inclined to go with the latter, since I had been shooting clays the day before, and had quite a nice tender bruise on my shoulder. If it is the latter, is such a consistent pattern to a flinch normal?
Any thoughts greatly appreciated.