No express rifle guy, but I do use irons more than most. PNW heavy timber on an overcast or rainy day...I've tried a lot of styles. My favorite is a military style broad post or black patridge. I take a jewelers saw, Harbor Freight 14 bucks, cut a tiny vertical slit dead center on the black face....paint the saw kerf very carefully with ProTec lure paint...plain old white. Gives a low light precise repeatable aiming point. A flat top deep fairly wide rectangular rear, imagine an exaggerated patridge pistol sight, enhances the sight alignment. I hate fiber, to my eye it's just a colorful shotgun bead, and about as precise.
Great info on the jeweler's saw, never tried that, might do it.
Sir Dennis's XS with peep and the gold Elmer-Elevation inlays with a flat-top-square notch sound great too.
That take-off barrel is buried in storage.
It would be an effort to dig it out for a photo of the little, filed and painted sourdough on that high ramp.
I might need to go through all my boxes of take-off barrels one day to look at beads.