I've got a 20 ga U1 DeHaan (Huglu O/U) that has a problem with the upper barrel firing pin when shooting doubles. It seems like on the first or second pair when I shoot for the first time of the day or after the gun has sat for a while, the first barrel (lower) shoots fine, but the second shot (upper barrel) doesn't allow the trigger to get pulled. There is some resistance and then the pin finally engages, usually well after the bird is past. After that, the gun works normally. The pins are titanium and I haven't taken them out for cleaning, because I don't know how, but I've shot cleaning stuff into them from the receiver end and blown out the residue. It doesn't seem to be dirty but I don't know if it's the pin or the trigger. Any suggestions?
Thanks,
Mike

Sounds like an intermittent obstruction. Probably a metal chip or similar object.
Have a gunsmith check it out.

The condition of the firing pins has NOTHING to do with the difficulty in pulling the trigger. The trigger should pull normally even if there was no firing pin in there at all.

How does the gun do if you shoot the top barrel first? My guess is that the trigger works (inertia block especially) needs a good cleaning with solvent. Then lubricate it well with Breakfree CLP or similar lightweight oil and try it again.