Hello,
I've never had the issue come up with my 45-70 GG loads, because I've only used IMR 4198 at fairly stiff loads over my 425 WFNGC. Good advice has gotten me to rethink things and I will be pulling back for deer hunting, likely going with something like 2400 when I can find some (and possibly a non-GC'ed 46-405M mold from Tom at Accurate).
The Lyman's CB manual (I'm looking at the 3rd currently, though getting the 4th), calls for a 0.5 grain dacron wad for most of the powders it recommends, including at the high end of each's loads. Taking 2400 as an example, I thought it wasn't very position sensitive. Is this a safety measure to prevent double charges, or is it truly to ensure adequate powder-primer contact? Is wadding necessary on any of these listed powders (entire load range low to high on Unique, 630, 2400, SR-4759, IMR-4227; and low end for IMR-4198)?