It's hard, if not impossible, to get a decent pattern from any rifled barrel. Even if the shot cup doesn't want to grip the rifling, the compression of the shot column upon firing swells the cup into the grooves, so it's going to pick up some spin. This spin is what ruins patterns.
Thompson used to make the Contender pistol in .410. It was conventionally rifled, according to law, but it had a choke on the muzzle that had straight "rifling" to cancel the spin of the shot column before it exited. It worked out pretty well, actually. That's the only way I know of to get a decent shot pattern from a rifled barrel.