Well, I don't have an answer, except to remember the old saying, "if it ain't broke.......". It's hard to imagine how that gentle pull-through cleaning could have done harm. Good luck. If it once shot that good, it can again.
The CPUMs don't shoot as well as before, but Polymags, JSB 8.44s, and Mako 10.5 slugs shoot fantasttic.
I thought it weird the CPUMS would shoot great at first, and now not so. Maybe they prefer a "new' barrel?
I'll have to add it to the list of things I don't understand, which is getting mighty long! The only thing I might suggest, shoot nothing but that pellet for a full tin, see if it comes back. And I assume the pellets are from the same lot, sometimes variances in dies will cause lot-to-lot performance issues.
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