I'm the newb, I've been lurking here for awhile and decided that I want to re-barrel my 300 wm into a 280 Ackley improved. The 300 is a Savage Model 111 and the new barrel will be a McGowen. I've already ordered it. They needed to know what I wanted, so it ended up being a semi custom order. As I was finding out the shank size I found I have one of the smooth barrel nuts. This started a whole new search on how to remove those! Anyway after I ordered the barrel I came across a little diagram of different action sizes. Now I can't find anywhere where it tells me if the two cases will work in the same action. Anybody here able to help me on this. If I screwed up then what action size am I going need.the diagram showed that you measure the opening of the action. Mine measured 3 3/4" All this research is kind of fun and habit forming. But my first attempt might turn out to be costly. Thanks