it was at 100 yards with a 6mmBR, i do own a chrono and i get a spread of about 15fps using varget. I do not measure run out. do you think that it what it is david? it does seem flyers ten to be up and to the left (10 o'clock'ish).
Honestly I don't know! I am just beginning to explore run-out issues and am far from an expert. I asked the question because this is the sort of phenomenon that is reported to be attributable to run-out.
I have read quite a bit of Barsness (and others) and their opinions seem to stand some long held handloaders beliefs on their heads. I have read that old factory ammunition typically has measured run-out as much as .010 - .011" (I don't have any old factory ammunition to measure). This old factory ammunition is often incapable of measured accuracy less than about 2" at 100yds. Modern factory ammunition is much better, typically run-out less than .007" hence the improvement in accuracy in modern firearms.
Typical hand loads are supposed to have run-out more in the order of .002 - .005", hence the large increase in observed accuracy. This decrease in run-out of handloads contributes (much) more to the over-all accuracy than the case being fire formed to the chamber. To get the tiny groups that we crave run-out must be reduced to less than .003", preferably less than .002".
I received my Hornady Lock-n-load cocentricity tool this past Thursday and began measuring ammunition. A favorite factory load for my 338Fed is the 180grn Accubond. It typically will shoot 3 shot groups around 1". Often 2 shots are touching with a 3rd opening the group to about an inch. I measured two boxes of this factory stuff - Most of it had about .004" run-out, but 1/3 of the rounds measured .006-.007". Hmmmmm....
I measured a warm handload (160 TTSX at 3030fps) for the same rifle that normally gives 3 shot groups 0.5"-0.75", but 5 shot groups always open up to about 1" or just under. Measured run-out was around .003" for most loaded rounds, but about 1 in 5 (4 in a box of 20) had measured run out of .005-.006". Hmmmmmm.............
Then I got to thinking. I have a Benelli R1 that delivers nearly unbelievable accuracy w/ factory 150grn Hornady SST ammunition:
I know, an autoloader can't shoot like that, but this one does. I never got around to buying a set of dies to load my own ammunition for it because as soon as I saw how it shot w/ this relatively cheap factory ammunition, I bought 20 boxes of it and let it be. So I pulled two boxes of the factory Hornady SST ammunition and measured them. out of 40 rounds, only 3 were over .003" and then not by much (.004"). Hmmmm...... (No, I do not think all Hornady ammunition is this good, I think I lucked into buying a good batch - maybe they just got through adjusting all of their machines...)
One of the neat things about the Hornady tool is that it not only measures cocentricity, it allows you to correct it. I corrected my 160 TTSX loads, some 200grain SST loads and 1 box of the factory accubonds all to less than .003". Unfortunately, I have not had the time to shoot the corrected rounds to see what (if any) observed differences there are. It's all just theory for me at the moment, but there do seem to be some observed phenomenon lining up with the theory. I'll know more when I have a chance to shoot some....
I would be very interested to hear of anyone else's experiences as well.
Regards,
David