I can't speak for the 223 & Shilen, but short chambered A&B/Grn Mtn barrels in 257 Bob and 7x57 both went to AI with no set back needed.
They are suppose to be .040" short, generally you only need .012" to make it an AI. Most people will go 1 full turn if trying to index sights or lettering on the barrel. Depending on your thread pitch that could be .062" or so.

Some is Good---More is Better----Too Much is Just Right