I think you'll find it a worthwhile project.
However, before you scrap the original barrel of the 700 action, try it out.
Secondly, get you a supply of the WC-860 powder. A while back I got 16lbs of it for $50 plus shipping from Widners. This powder should work well from the .338 with 250 and 300gr Bullets.
It has proven to be THE best powder for my .300Rem. UltMag.
I picked up a used Savage M110 for a pittance. Nobody wanted it because of the $60 a box ammo. I thought about the surplus .50BMG powders and the availability of the 180gr Remington Corlokt bullets for somewhat less than the cost of other bullets.
It works out that the Remingtons ARE the most accurate bullets too.
I've got a load of 107.0gr of #860 and a 180gr Rem.CorLokt that will shoot sub-moa for 3-shots. It chrono's 3,350fps. And, cost less than most accurate .308 ball loads. Performance of the 180gr CorLokts on game has been quite satisfactory. Not nearly as "explosive" as I initially feared.
For some reason this rifle despises the 180gr Nosler Ballistic tips (3" groups), and isn't too fond of the Sierra 180gr ProHunter or GameKing (2-3"groups). I do plan on trying some of the 190-200gr class match bullets sometime. Other good powders have been Retumbo (velocity), and Reloader-25 (accuracy). H50BMG was dissapointing with low velocities and high sd's. H4350 and H4831SC as well as RL-22 weren't anything to get excited about.
You'll find the Remington brass to be good. I ordered 100pc. from Midway before the latest price increases last year. They've gone up a bit, but are still a LOT less than the Lapua brass for the .338Lapua. I neck turned mine but it really didn't need it. I only turned it enough to "uniform" the necks.
I think you may be a little dissapointed with the .338" bore however.
I've got a .338/06 that I built several years ago. It's a great rifle, but the substantially greater cost of the bullets "takes the edge" off of wanting to shoot it.
The only drawback to my .300RUM is that it DOES RECOIL !!!!!
My rifle has a 26" sporter barrel and weighs about 9lbs with the scope mounted. I took off the slim hard rubber pad, and cut the stock and installed a "Kickeze" pad. That took away some of the pain of shooting off the bench, but I still lost the hide off the bridge of my nose when shooting a deer from a sitting position. So, beaware that you will get some recoil..............
The Rem. Ult.Mags are very well laid out cartridges and the only thing "extreame" about them is that the level of performance is only slightly exceeded by the .30-378WbyMag, and the .340-378wbymag. (.300rum and .338rum repectively). I personnally see the .300RUM as little more than a .223Rem scaled up..... a lot !!! (Think a 180gr .308" bullet at the same speed as a 55gr from a .223).
As a "poor mans" alternative to the .338Lapua, I think that you'll find the .300RUM a better alternative due to bullet cost.
Yes, you'll need to use the .338" bullets. The .339" comes from the rounding with the metric conversion of metric diameter bullets to .338". I had considered "playing" with a .338Lapua but action and brass cost didn't appeal to me.
