[higgite]

I measured the difference in case volume using the water method between my Starline and Nosler cases for 6.5 Creedmoor. These cases were all full length sized with a body die and neck sized with a Lee Collet die and trimmed to the same length. The difference averaged .003-.004 grains.
What scale are you using to measure to a thousandth of a grain?

Is this difference insignificant enough to just run both with the same load?
If you really mean .003-.004 grains difference, that is essentially no difference. But, I'm skeptical of your measurement, no offense intended.

Or should I work up the load by downloading a few tenths of a grain and working back up again?
Yes, like Don said above, you should always work up a new load when changing components, but especially in this case because .003-.004 grain difference just isn't realistic.

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