Man there's a term I haven't heard in a coons age! I had a few of those "progressive twist" barrels back years ago for a couple of my bench queens. They honestly weren't worth the added expense. They did last a tad longer as the throats didn't get blown out as quickly. But I only saw around 20fps on average faster than a standard twist and little to no effect on accuracy. Never tried one for a smoke pole though. Thinking about it, you may be on to something lemoyne. They probably would be better with a big bullet weight. Would probably be especially good for a full bore connie.