"...because of the build up..." Get a small foil roasting pan or any large can. Fill it with solvent, drop the whole bolt in and leave it there for 24 hours. Blow it out if you have air. Canned air is expensive stuff, but you can get it in a computer or electronics shop. Brushes and pipe cleaners otherwise.
Neither grinding the bolt handle nor solder will do anything to the headspace. Solder is too soft and the handle has nothing to do with headspace. You don't need to adjust the headspace anyway.