So you're saying that if I start out with, say, FGMM and shoot a group of them, then switch to BH 175's, I'll have to shoot a number of rounds with the BH's before starting to group with it? Why is that?
I can't explain it... I have fired enough 10rd groups routinely, to notice a trend in groups tightening up ( from the first shoots, then settling in for the last shoots. ) when changing ammo brands .
So basically my 10rd groups would slowly tighten up, then settle in for the last 5 rds.
I will say, not every factory round would do it.. but there certainly was enough of a trend to distinctly notice it.
There used to be a CMP list of what powders not to fire after one another... IE when using a different load /powder for inside 300yds, followed by a 600yd different / powder load.
So as far as I can tell... it has to do with the powder.
And again, I have no scientific proof.. but just have noticed it from the various factory load testing I have done.
I usually will spend all day doing those "factory" load tests.... so that has also helped make it "easier" to see.
Next barrel I test for precision with factory rounds ( a 6.5CM Kreiger ) , I am going to note the order of firing, and record that info.