Ron,

To get the psi maybe a bit difficult. The 375 flanged is essentially the 375 H&H mag. IMR shows pressures ranging from 43,600 CUP to 53,000 CUP for the mag.
http://data.hodgdon.com/cartridge_load.asp

You can call IMR and talk to a tech.
7:00am to 5:30pm Central Monday-Thursday : 913-362-9455

Wright shows 18 tons for the flanged, page 271.

You could purchase a PressureTrace Internal Ballistics System and measure it yourself.
http://www.shootingsoftware.com/mm5/merchant.mvc?Screen=CTGY&Store_Code=RSI&Category_Code=PT

Or you can purchase Quickload for the calculated pressure
http://www.neconos.com/details3.htm

Pete

http://www.damascus-barrels.com/Movie.html