In my .243 Long Range rifle (Sendero profile)(1-10 twist intended for less than 105's) 58 gr. Hornady V-max factory ammo shoots sub 3/8" groups at 4100 fps (26" bbl) it also shoots Fiocchi 100 grain ammo into sub 1/2" ammo (I had this left over and used it to sight in and took 2 shots and they were touching so I decided to shoot the group; I was shocked). It Hates 95 SSTs , 75 V-maxes are ok. I really wanted the gun for long range Prairie dogs and it is a laser with those 58s. We have prairie dogs the size of ground squirrels in AZ and my best calculated shot so far was 735 yds. These pdogs are barely 3" wide. Anyway, if a gun shoots any load super accurately it shows you that it is indeed harmonics because everything else is consistent. AND just because a factory load doesn't shoot well doesn't mean that you can't get that bullet to be accurate (Repeatable) at a different velocity or with a different powder burn rate.
I have 3 -243 rifles, the one I described with 26" bbl, another Winchester 70 with a 24" heavy bbl from the 70's and a HOWA 1500 sporter 22" bbl and they all like Remington 80 gr. corelokt SP and HPs, sub 5/8" groups. That was my Woodchuck killer in the wind. Would obliterate woodchucks, especially with a boney impact.
I have a 220 swift and everyone told me I would never get 40 grain bullets to shoot well. So far 40 gr. Nosler ballistic tips were the most accurate load I came across (so far) with H-380 powder anywhere from .005, .010 and .015 inches off the lands and settled on .010, slight variations in powder weight affected the groups. My best 5 shot group was .306" and several were 7/16" or less, but best velocity and accuracy was the .306 group at 4177 fps Avg. sighted in at 265 yds MPB zero for a 3" diameter target.
I say it is harmonics.
