I’ve had a few brand new double shotguns and they were stiff as stale jerky.
My cure has involved snap caps, lube as normal, and work. Works too, and faster than you’d think. I’d listen to Mr Peacocke.
What did he say? Pressure smoothing.
Nowadays I use Molykote spray on areas with visible polish but limited pressure. Locks too. Good grease goes on the hook and the underlugs where theres plenty of pressure. This is both on vintage and newish break-opens.
Lately I’ve been breaking in a tight and gritty feeling 550 and that guy gets molykote on the mag ramp, all bolt external friction points, and a little light oil and molykote in the sleeve. Then I sit on front of the boob tube watching safari videos, annoying wife and dogs, cycling cycling cycling, and at times pulling the trigger on Mr Dagga. Aaaand, it works! As the man said it’s about polishing some microscopically high spots, which is what, bending down some peaks, not removing material.
Huge fan of dry lube now since I had a Model 12 gum up on me in the duck blind. Found the dry lube, cleaned off any petro lube, dry lubed the bolt, action and trigger group, problem solved.
This started as I was thinking about dusty old Africa so I called up the chief gunsmith at Griffin and Howe, having already decided to experiment with spray graphite and molykote, he fully endorsed and recommended this known approach, so am not exactly reinventing the wheel.
Now: Messy, unpretty. Effective.
Next, trials with moly grease, moly paste.
Away from extreme cold or dust!