Sounds like you are looking at a 2 groove rifle which shoots a patched conical bullet with wings. If you have the mould, you should be in good shape.
The twist will be slow, so that the bullet will not strip out of the grooves when fired with a healthy dose of black powder.
This rifle design was dubbed "Express" by Mr. Purdey, because the larger amount of powder used (as compared to a ML bore rifleof the day) with greater velocity and flatter down range flight.