!. It has happened in the USA at reenactment displays, with severe and lethal results.
2. The MLAGB do not discourage it, they positively prohibit it. They also prohibit the use of BP substitutes in the comps.
3. The international federation of muzzle loading - the MLIAC - prohibit it.
Pyrodex and all the subs should be used by volume. However, to set the volume initially, you still have to weight the charge of similar grade BP to get the equivalent volume. Having established the volume of, say, 70gr of FFg for your Enfield P53 and set it on your powder measure, you can then substitute it for the, uh, substitute. IF you weighed it, you'd see that it actually weighs less.
tac