I remember seeing this thread yesterday, came back today to read more of it. Half was just to see what the deal was w the "18 inch 300 RUM". Knew it was 50/50 on whether it was canned versus typo (28" v 18" easy slip).
Sounds like a decently wild setup, but it also sounds like OP has a pretty good idea what hes doing, has thought thru the relevant details / issues... which is usually what it takes to make a setup like this run well. Im going to guess the OP will have pretty good (or better) success with this.
While this isnt a combo that fits my particular needs, i think it sounds pretty cool, i respect it, i like it when people push the boundaries some, run a setup thats a bit "out there" for a lot of people but "just right" for their needs.
The 1-8 twist is probably a safe move, if a particular bullet isnt performing how ya want, i dont think will have to wonder if it wasnt stabilised enough.
Anyways! Hope OP keeps us updated on how it works out
id like to hear about velocities too