IIRC, the .318 is not very different from either the .30-06 or the .338-06. "Ken Waters' Pet Loads", 6th ed., has case forming instructions on p. 1010. You will probably need the FL dies and a tapered expander pin to make the case from .30-06, and you may need to trim the cases, but that is all there is to it. UNLESS you have one of the odd square-shouldered .318 WRs. If you have a square shouldered chamber, that should confirm manufacture by WR, but I do not know what you would do about reloading.
My first suggestion would be to see if an empty .30-06 case will chamber. Use a new case if you have one. If the case chambers, try firing a BLANK load, the sort used for the initial case forming of some wildcats. I would also suggest a chamber cast and slugging the bore. I suspect you will find a 0.330" groove diameter.
The .318 WRs claim to fame was a long 250-grain bullet. Bullets will be a problem. You will need to squeeze .338s down to .330, and that means custom bullets at $2 each or obtaining bullet swaging dies and a very powerful press to use them properly. About 20 years ago, I made some 250 & 275-grain bullets for the .338 from copper tubing and lead wire. I used a press intended for reloading .50 BMG and such cases and a 4-foot piece of steel pipe on the press handle as a cheater. The process worked, but only because I am reasonably strong. The same degree of effort may be needed to swage .338s down to .330. An arbor press (or the jack for your car) may be needed.
If you intend to shoot the rifle a lot and are not worried about collectability, you could re-bore & rechamber to .35 Whelen or maybe to .338-06. That would be a lot less hassle, but less fun.
