The shells produce standard SAAMI pressures for a 12ga. There is a warning on the box to NOT fire them in plastic 12ga signal guns. They should work in the old-time all-steel 12ga (or 25mm with reducer sleeve), but then you have committed a federal felony. A 12ga single or double, cut down to the legal minimum, would be darn handy, though.
So, winmag, when I'm looking to buy a gun in a few months, mind if I ask you for a few suggestions?
Absolutely, regarding the double or single legal length doubles or singles, but I was wondering about the older vintage doubles, not the damascus variety as those have well discussed elsewhere. A friend has a couple of 20/12 adapters he uses in his grandads old shotgun.