The experience in the shotgun-only deer hunting areas of the US seems to be that rifled chokes don't stablilize rifled slugs well enough. That's why the majority of deer/bear slug guns have rifling the entire length of the barrel. I thought of getting a rifled choke for my O/U for those cases when while bird hunting a pig shows up but was told at a S.H.O.T. Show that it simply wasn't a good idea . . . and this was by a manufacturer of chokes! Unfortunately, I can't remember which one. My guess is that if you had a shotgun whose barrels were tapered and regulated to cross at 70 yards instead of 20, you wouldn't need to worry about rifling in any case. Just put a pair of Brenneke's up the spout and let fly. Whether this would really be possible might make for some interesting (and rather costly) experimentation.