I know refinishing is frowned on (by me too) and most cold blues are a bit hit and miss, but in case anyone is interested I think I got some ok results with Phillips Professional Cold blue:







And before:







In my defence I think tatty enough to make a refinish justifiable

Obviously not as good as hot blue but not too bad I think

My two learnings were (1) acetone for degreasing and (2) check the blueing solution carefully for the rear sight riser screw before you pour it down the storm drain. Unless you enjoy spending an hour going through the silt trap with a magnet of course