You can easily paper patch .416" cast bullets, smooth or grooved, for the .423" goove diameter barrel.

As 9.3 suggested, the Lee sizer die would be necessary for reducing them to the correct size.

Full power loads can be used with paper patched bullets of WW or slightly softer metal.

The paper patched bullet needs to be lubed first, before running it through the die. Polishing the die first with Flitz or auto polishing compound is a good idea. Shove them up through the die nose first.

Doing this for this particular calibre is no different than for any other.

Oh yeah - no crimps as that tends to cut the paper and then lead the bore. A very sight taper crimp might work, but best to have no crimp and use a slightly faster powder. Velocities might be as much as 100fps faster than equivalent loads in jacketed bullets.