You want to underbore to prevent rollout. Accuracy is more of a function of quality paint and a clean barrel.
If I was buying barrels today, I would want something in these sizes:
.690 (most stock barrels are around this size.)
So, three new barrels and maybe hold off on the .685 unless your paint is largish.
The key here is having a barrel tighter than the paint you shoot. So you need to figure out what size your paint is locally. I'm in San Diego and all the paint I shoot calls for a 680 or 675.
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