Holland's .240 Flanged used 38 grains nitrocellulose (not Cordite), and a 100 grain spire-point or semi-pointed bullet for 2775 fps in 28" barrels for 15 tons BaseCup, 46,400 PSI.

There are many British rifles marked as proved for Cordite that are chambered for cartridges that were never commercially loaded with Cordite. The .240 appears to be one of them.

I think I would carefully work up to standard velocity (as adjusted for barrel length) shooting over a chronograph with maybe IMR 4350 or IMR 4831, and standard primers. If the rifle has 26" barrels, I wouldn't exceed 2700 fps. Remember that by the time you've got conventional pressure signs, you're already in trouble.

This cartridge is available commercially from Kynoch. I'd probably check with them (David Little is the proprietor) about load data. I'd probably want to shoot some of their ammo over a chrono for a benchmark.