If Merrington says they're ok, they're ok. Your loads were very conservative. When you say pinholes, do you just mean small pits? Not true holes?
If we all stopped shooting anything with pitting it would take a lot of guns out of use. I think Flintfan is correct. Shooting may have made them more visible.
I do have one set of pitted barrels that I won't shoot. A set of Greener barrels that are perfect on the outside and heavily pitted inside. I temporarily modified my wall thickness gauge by gluing a conical brass point onto the "ball" that goes into the barrels. This went into the pits and I got readings of 16 thousands in many places. And I realized the pitting might be even deeper. Fortunately the gun has a second set of barrels that are fine.
