The wax slug while still not the greatest idea, is a great deal safer than the cut shells as the diameter of the shot charge is within tolerances for the bore and throat areas.
You may still have an issue with tighter choke constrictions but using softer wax, it will allow some compression movement that you don’t get with the cut shells.

Cylinder bore is the best choice here.
If you feel the need to use a choke tube, use an external constricted turkey choke.

As I recall, there’s some interesting data on another website on slugs, will post it in am when I’m not on a tablet.