Seeking some help from forum members if possible.

One of the hammers on a non-rebounder double I have is proving quite "sticky", in that when it is pulled back to full cock (either from half cock or all the way from resting) and the trigger then pulled, it occasionally only drops so far down as the half cock rather than completing a full drop to hit the striker.

I have had this expertly seen to with the as-original locks being fully removed, oiled etc but I fear the issue may be returning. We initially thought it may be wood shrinkage etc when the gun was taken outside, but it has happened in indoor temps as well.

Has anyone any experience of this as I would appreciate some thoughts/solutions?