I hace come across two OUs that had hammer-sear problems, one of them doubling. The first was due to dried oil which slowed sear movement and prevented cocking the top barrel. Ever since that expreience I stopped using drying oils, anything with thinners in it which evaporates and leaves a gummy residue.
The second was a double trigger OU which had some stock shrinkage that was "fixed" by overtightening the grip screws. The tightening moved the trigger plate closer to the top tang and the gun doubled.
