I'm looking at buying a 29-4. It has a very prominent arch shaped drag line on the recoil shield where the back of the cylinder contacts it. All my revolvers have this, but to a lesser degree. I don't believe it has a high round count as the drag line on the cylinder is barely perceptible. Is this cause for concern?

No. That's the locking pin dragging when you close the cylinder. I put a touch of grease on it after cleaning.

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Science plus Art

Also check the pin for machine marks.
I've seen a few that had rough machine marks that caused an excessive drag line.

Thanks for the info. That's What makes this a great site - especially for novices like me.