Help me read my OCW

[bfk4lyfe]

Rifle: AI AT with brand new Proof 24” 260 barrel (had 60 rounds through it before today)

Load: Virgin Starline, CCI 250, Reloader 16, Hormady 130 ELD-M. Approx .035 off the lands.

Loaded up 42.3 through 43.5 in .3 grain increments.

Results:

I know I’m looking for similar point of impact, and to me it looks like 42.6 and 42.9 are the same. What should my next step be? What can I do about the SDs? Does the virgin brass and low round count on the barrel have anything to do with that?

 

[spife7980]

Depends on how much more brass you have to form. It would be easy ti just pick one and finish forming the rest of your virgin brass if you only have a little to go. If thats not the case and you have lots to form still then I would test 42.7, 42.8, 42.9, 43.0, 43.1 as Im picky and want to make sure its actually doing what I think it should be.

 

[leftyk82]

Does the virgin brass and low round count on the barrel have anything to do with that?

These are factors that are both temporary and, yes, could have an impact on your testing.

Your barrel will likely speed up once it has 100 or so rounds. The brass, once fired, will be fit to your chamber. I'd say your testing can begin in earnest now but refined once you get loads with fire formed brass.

 

[Milo 2.5]

I'd test 42.6-43.0, by 43.1 you are in scatter node. Your velocities are in check for a speed up, I would only concern myself with the barrel speed up and not worry about fired brass. Most likely fall into place, if not a minor charge tweak may be needed.
If it was me, I'd lose the magnum primer, your case nor your charge warrants it and it could prove to be detrimental.

 

[ShtrRdy]

I agree with your assessment. Pick 42.9. The new brass can have an affect on your results. If you have some more new brass try loading 5 each at 42.7, 42.9, and 43.1. See if this will repeat and if the sweet spot favors a little more or a little less then 42.9.

Once your brass is all fire formed you'll need to tweak your load slightly to keep it in the sweet spot.