The 300 lapua improved has a little over the 300 Rum but you are going to be looking at finding a action to handle the larger boltface, going to have to find or have some dies made, all of the pains that go with any wildcat and all for little gain. That said I have built a couple of these and love them. I am a lapua brass fan. My personal 300Lapua AI is not even braked and is manageable in a 12ish pound rifle. I built it because it was the action I had on hand at the same time I happened to have a fast twist 30 cal blank and a reamer. I have not been disappointed with it. If I were you I would just go with the RUM and enjoy, lots less hassle trying to feed the thing leads to more time to shoot.