NE450No2:
What do you mean by "watching for pressure"?
This is dangerous advice for a reloading novice:
the first signs of dangerous pressure in a Brit double may well be spontaneous violent disassembly a few inches in front of the shooter's face!

The proper advice is to shoot over a chronograph. With powders in the medium-slow to slow burning rate, loads which do not exceed the published muzzle-velocity of the original cordite loads will generally be safe in a Brit double.