Since the adapter is 2.75 inches long, and a most handgun calibers are going to be an inch or more shorter, I expect the adapter is rifled in the non-chamber section, giving it enough spin to fly straight out of the barrel without hitting it. Be cool if they could add a stepped down, longer barrel that would extend into the shotgun barrel, providing 6-10 inches of rifling.
2 3 /4" of rifling isn't going to be long enough to stabilize much, for any serious type of accuracy. say the rifling area was 2 1/2" with a twist rate of 1:10, 1 complete turn (revolution) in 10", that would be 1/4 turn/spin. it might be feasable for using a smaller shotgun guage/round in a larger guage gun. sounds gimmicky, not accurate and a waste of money to me. some quality shotguns have used full bbl insert sleeves for years that work well, but they are not cheap, and add wt.
here is a video of a guy shooting 44mag thru 22lr and also has a 9mm rifled insert. https://www.youtube.com/watch?v= http://youtu.be/3l4PBOQT1dg
a 44 caliber round thru a 22 caliber bore? sounds like a golf ball thru a garden hose. sure it's not the other way around.
