semi custom and tack driver dont always work in the end result.if half" to a little under 3/4" works for you buy a tikka factory gun.this is in relation to your wanting a 300 wby.you also have to take into account your honest ability behind this gun.i could name you a # of quality smiths that are on a little less costly work.very capable.how much do you have to spend approximately.also yes they can all build a half inch or better rifle.rifle capable of 1/2 inch or better.
My factory Weatherby mark v was very accurate until I had a brake installed. I'd guess it changed the node. Best it will do now is sub moa which is fine for hunting. If I started playing with the load I'd guess I'll do much better but I have neither the time nor interest currently.