The OPs original post said that it could be any of the three shots, not necessarily getter hotter but different temperatures.
SoTexCurdog, does that mean if you let the barrel cool sufficiently between all 3 shots that they all group together?
Yes, it has appeared to on more than one occasion.
Also, sometime ago I read about and tried a load development method called OCW. I believe it is an acronym for “Optimal Charge Weight), where you basically do that same thing but shoot one shot of a progressive charge weight at “X” number of targets for each load you have. You end up shooting the same 3 loads at the same particular target but you don’t shoot the same load in succession, it progresses then you come back full circle and shoot another progressive string until all three loads have been fired at the same target.
Anyway when I tried this OCW method, I allowed the barrel to cool to ambient temperature before each shot, and the 2 tight shots/one flyer grouping seemed to disappear for the most part.
I also need to mention that none of my rifles are bull barrels but are of various sporter contours with the only exceptions being 2 Winchester M-70 Coyotes with what the factory calls a medium bull barrel. These two rifles also seem to buck the “2 tight shots/one flyer thing, but again, not always.
I agree with MD that there are so many variables but this type of grouping happens far too often with too much consistency in so many of the same rifles even after having tinkered with the stocks, scopes, loads, etc. I have spoken with and seen it happen to other shooters as well.
Back in the 1980s I had a 270 W. that I hunted with, every year before hunting season I would take that rifle out and fire one shot at at 100 yards and one shot at a 200 yard target. Every time I did so that rifle would put the shot at dead center at exactly 3 inches high at 100 and approximately 3-1/2” high at 200 yards. It never failed to do so. I went out and shot my limit of deer without missing a shot. After about 5 or 6 years I decided to do some target shooting with some remaining reloads I had. When I did I quickly found that this particular rifle didn’t keep that same accuracy with the additional shots. It did the same 2 tight/one flyer thing. But instead of the first two shots being in a tight group, the second and third shots literally went southXsouthwest and dropped down and left a good inch and half at 100 and slightly more at 200. After letting the rifle cool a spell, I fired another string and ditto, same thing with virtually the same identical pattern. It did that several times in a row. Now, it could be said that existing barrel fouling caused that to happen but I vigorously cleaned the barrel with the predominant solvents of those days (Hopes #9/Shooter’s Choice and some JB Bore paste) and fired some more 3 shot groups. But it didn’t make any substantial difference. The groups were pretty much the same.
