The .338 max's out at closer to 63,000PSI, I think. The trouble with pressure #'s, is there are three different indicators used for the same actual pressure.
: CUP is copper units of pressure.
: PSI in the States is a transducer reading of direct stress chamber pressure.
: CIP in Europe, I don't know what the letters stand for,(maybe 'copper indicated pressure'?) but they list the end result as PSI, ie: CIP = 56,000PSI;
: In the States, the old copper crusher method would list virtually the same pressure level as 55,000CUP(or 56,000CUP) and if a transducer was used, 63,000PSI - all the same load.
: Trouble is, people mix up the #'s and names and it's easy to do.
: CUP does no co-relate to PSI, as a max CUP for the .338 is probably somewhere around 52,000 to 56,000CUP. This is actually closer to 63,000PSI (US measure) but is around 53,000 to 57,000CIP's PSI - rather confusing, isn't it.
: As far as I know, only the .45/70, .450Marlin and .44 mag have identical #'s of both CUP and PSI(transducer). ie: 40,000CUP is also 40,000PSI. The .458 WM's numbers are close.
: You should be able to get close to 2,400fps or a bit over with a 300gr. in a 24" .338. The correct powder, of course will have to be used and ther are a lot of them in the burn rate required.