I didn't think one could get full constriction out of jug choke. Most of those Soviet MU or MC guns with such "wine cork" boring were skeet guns, no?
There must be an Englishman behing this "....the barrels have been modified....". They are good at saying things like your wife has a lovely round face instead of saying she is fat. She is a wonderful cook instead of saying she is pathetically ugly.
Please note there are shapely women with round faces and pretty ladies that can cook.