Unless you're going for match grade accuracy don't waste your time and money sorting and buying all that equipment. 2"-3" groups at 200 yards is more than adequate for hunting.
When you say you neck size only, did you purchase a neck sizing die or just back out the sizing/decapping die slightly. If its the latter then you're not neck sizing you are partially sizing. Big difference.
I've loaded for the .243 for about 55 years now. This cartridge is notorious for case neck stretching. You should check your overall case length every 2-3 firings and trim as necessary. Upon firing the brass flows forward. Also watch for brightness at the web of the case. A sign of thinning brass and a possible case separation. True neck sizing can reduce this a little.