Appropriate fit of bullet to bore.

I'm looking for someone with experience shooting lead conicals in muzzleloading double rifles. I have a Lang double in 18 gauge (about .635" across the lands). The barrels' twist rate is about 48-50" suggesting that it would shoot conicals well.

To do this I need to have a mold and bump die made to produce a bullet that will be small enough to load but large enough not to shift in the second barrel when the first barrel is fired.

So, can anyone give me first hand knowledge of bullet/land-diameter tolerances? I would greatly appreciate any data that you can provide.

Thanks,
Brent
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...never pay Dave "one more dime" (thanks Stanlie)