I am thinking about ordering a mold from Accurate for my 348 based wildcat.
what I am not sure about is what size the nose should be on a bore riding design.
I am looking at their designs number 37-285C, 37-285D, 37-285H and 37-300C. I would want any of these modified to remove the gas check. 

My intention is to load it over black powder, so the bore rider seems like the ideal way to go, so I can keep a wad in the case neck without causing difficulty with loading.

Any thoughts or advice is appreciated.

Jesse

Think you posted the dimensions of your barrel in your other thread. You answered you own question with that bore-diameter measurement. The .348 has a longer neck then I recalled, so that should not present a problem and it should make a great BP round. Good "wildcatting" on your part. 

If you are designing your own mould you might want to go with a reduced first band, as well. Nose at actual bore-diameter and first band 0.001" larger. What I do with my 38-56 (similar BN cartridge) is load it long enough that I generally use the Arizona Sharpshooters loading tool to push the cartridge/bullet into the lands at least as far as the first driving band. Another thing that I've learned to do that helps with accuracy is use a bushing neck-sizing die as the last step in loading. Puts just a hint of tension on the neck (can still turn the bullet by hand and pull it out with some effort - I thumb-seat my bullets). All of this seems to square up the bullet with the axis of the bore, is my guess. Something akin to breech-seating with fixed ammo. 

Am guessing that you will find 2F Goex to work the best in your cartridge. The reason being that 3F Goex or one of the Swiss powders may give you too much velocity with cast bullets. This is assuming that you are after the best accuracy rather than the highest velocity. My 38-56 loads are running right at 1400fps muzzle velocity. Any faster (can easily get in 65gr of Swiss) and leading rears its ugly head. As long as the powder is into the neck the load works well. Am using multiple wads to get the bullet spaced out to the correct cartridge OAL in my chamber. 

Have fun!! Is a great ride getting these things to perform at their potential.