Zippy, thanks for the info on the 10 gauge.
Good ideas in the last post, trying a shorter BBl and then adding a stack of baffles on top of that with a retention plug at the end (think threading internally as for a removable choke) might be an option. The trial BBL would be unported as a test-mule for extraction. Great idea!
It's lathe-time... might try .357 just to get more internal volume.....