Champion shooting master

I was patterning my uncles old (1947) rem. 31 pump with the champion adjustable choke made in Gardner Ma. and was surprised with the really nice patterns. Anyone have any experience with that device.?? Its a collet type like a poly choke but it has venting before the charge goes through the restricting collet. I was nervous at first because my inside mike only read .015 thou restriction on full but the gap acted like a recessed or jug choke. I have yet to count pellet holes but it looks like a very even 80 percent at 40. The adjustments on the barrel are marked in yards not degree of choke. Frank C.