I'd say that performance is similar in the 300 grain Sierra bullet class. I've had custom rifles in both chamberings and other than brass life they're it's not worth discussing the balistic differences.
338 Lapua brass is $130 at Sinclair or Brunos Shooters Supply both if you buy 100 rounds.
My buddies factory 26" bbl Rem 700 338 RUM is pushing 250gr Sierra GK's at barely over 2800 and still getting slight pressure signs with RL25. I have the load data filed if you want it. His were seated to load in the mag at 3.65" OAL.
The 338 Lapua is superior with its better brass, also it can be improved quite easily too.
Get a 30" or longer bbl if using either, that would be my recommendation.
you can get Federal brass for them BUT, you have to buy loaded Federal ammo to get the stuff... not sold in bulk anywhere. If Federal ever makes it in the High Energy version, I'd get that stuff for sure.
I easily got 200 fps faster reloads in the HE brass than their standard stuff in my 338WM. 250 Barnes X bullets at 3050 fps vs. 2800 in the other stuff... with the same load. Remington and Winchester were all the same too.
I lost primer pockets in three to four loadings but other than flattened primers there were no other psi signs at all. I'm sure the load was in the low to mid 70k psi range though.
Both 338wm's I had would group under .7 moa with those top loads too, my buddies still does. I jumped up the the Ruger 416WBY because I knew I was pushing the pressure and still wanted the same performance with a little more safety margin though.
Its an A-Square round. RCBS sells the dies you can also get custom made brass for the same price as from the factory from Quality Cartridges.com. That speed came from a 29" barrel. The cheapest way to go about it would be to use a CZ550 safari 416 action or something that was chambered in a 378 or 460.
i talked to a guy in ohio who routinely builds them on savage long actions which start life as a 300 rum, really impressive, i was concerned about the strength of the unit, but his has lasted well, and all of them have had zero problems, but the wall thickness of the barrel was an issue for me, and i was thinking of moving to the 338 rum instead, the pressure and size of the case is identical to the 300 rum, the only difference is the bore, so i was considering doing that instead, and having a thicker wall of metal around the cartrige would give some peace of mind, if the rounds perform the same, or very close, it would be great
i would like to end up with a 250 grain bullet in .338 cal moving at 2900-3000
.338 RUM is cheaper to start off in than Lapua. I had thought that the RUM was a belted Magnum case but recently I found out that it isn't. (good for Rem-Chester, dies are probly easier to get ahold of, ammo might be bought locally if needed, more rifle choices, less money per rifle if bought stock and not custom made.)
Brass is cheap for RUM, then again Lapua doesn't offer RUM brass, yet anyways. Rifles are cheaper in RUM, they can even be bought chambered in RUM and the price still comparable to the other bolt actions. (Cheaper price due to the manufacturer not having to design a new action for the round.)
The RUM is relatively new compared to the .338 Lapua, this is probly some of the manufacturers answer as to why they don't offer the .338 Lapua. (Make money without having to spend it to retool or R&D... design a cartridge to fit the rifle and not design the rifle around the cartridge...)
I have a Lapua, which was the in-between cartridge between the .300WM and .50bmg, then that oversized .408 Chey-Tac came out.