Bolt head sizes?

I fit my FP/striker protrusion between .040 and .050

Something else to consider in addition to striker protrusion is bolt head lift in a properly fitted bolt/striker combo.

At about the last 1/2 to 3/4 turn of the screwing in your bolt head you should have the cocking piece begin to lift. Clearance between the cocking piece and rear of bolt body should be around .016 and .060

The reason this is done is to prevent the safety stud of the cocking piece and from contacting the the long cam in the groove of the bolt and potentially damaging/ destroying it or other hard work that's been accomplished like lug fitting.

If the striker is to short, reduce the collar at the front of it. If it's too long adjust the receiving surface manufactured into the rear of the bolt head tenon.

Make sure the threads at the rear of the striker fit the cocking piece tightly to prevent them from wandering around inside the cocking piece which causes inconsistency in pull off and is cumulative to other poor fitting techniques.

The hemispherical shape of the striker where it protrudes through the bolt face should also be carefully examined for safety. If the shape is malformed to where it allows gas leakage to get past it where it meets the bolt face it could be hazardous, if its pointy the possibility of a primer pierce exists and the port in the front of the bolt face should be carefully examined to make sure its not pitted damaged or worn to where it has excess clearance.

Vickery's book has additional information for firing pin fitting for both rimmed and rimless cartridges across the board for various weapon types and contains additional reasons for fitting that are often overlooked or not considered by many so called professionals/gunsmiths.