Hoping you or others could help.
Shooting my pre64 M70 .264 Win Mag and trying to find a good hunting load for it. I've been working with the 140 gr. Nosler Partition primarily, but based on your comments in the other thread on the 264 vs. 7mm RM, I purchased some of the 129 gr. Nosler Accubond Long range bullets.
Went to the range yesterday with 4 rounds each loaded with two different charges of two different powders (total of 16 rounds) with the Partition. Because I was out of time on the loading bench, as sort of an afterthought, I also loaded 4 rounds of the 129gr ABLR with a single powder charge. I shot all rounds loaded and for the most part, I was pretty happy with the results.
However, here is my question. In all instances, I would fire the four rounds of each loading one right after the other for grouping and then I would let the barrel cool for maybe 20 minutes before I would fire the next four. I usually only fire three rounds, preferring not to let the barrel heat up too much, but in this case I amended my usual routine to fire all four. In the majority of these 4 round strings, it seems like the first round would hit maybe 1-2 inches above the other three rounds. The other three rounds would usually group around 1 in., but the first shot, of course, would enlarge the group considerably. This happened almost religiously in each string so I'm wondering what might be causing this?
My thought is that once the barrel heats up after the first shot that it tightens in the stock and thus everything stays the same after that. Do you agree? I have tightened down the fore-end screw to a known torque level already prior to shooting. Maybe I should try torquing it down some more?
By the way, other than the 1st shot flyer, the single load with the ABLR bullets went into a 3/8" group, which was mighty impressive. I usually can't shoot that good. The flyers are disconcerting, though.
