6878mm,
In a way it depends how you or your gunsmith plans on tightening the gun. If your hinge pin is in good shape and you can get away with simply building up material on the barrel hook or lumps with weld then I would wait to do so after case coloring the action as slight dimensional changes are likely to occur. If you have to replace the hinge pin due to extreme wear or maybe because it's easier to do so with some hammer gun actions, then you should do that prior to case coloring so that you can fit it while it's fairly soft. Once the action is case colored, regardless of hardness, you don't want to scratch it or rough up your fresh case colors from handling it while you fit a new hinge pin so if that's your route do it before you case color it and then do whatever minor "hard fitting" you have to on the barrels if it changes at all dimensionally after case coloring. In most cases I think you will find the first method i mentioned of building up material on the barrels is more often the chosen method. I hope this helps,
Channing Will
