In theory, the cordite Could cause a difference, but as millions of rounds were loaded and fired with N-C powder, and we have probably all used surplus so loaded, I don't think it is a real problem.
The bullet is critical. By that I mean it should be as close as possible to the Mk V11 in design, and if so, will stabalise with the right powder.
As we are mainly using well-used barrels, I also think .312" or so could be a help!