since the PM9 has polygonal rifling, would that mean a person should not shoot lead from a PM9
I would think that to be the case -- at least you would have to "de-lead" the barrel very often. You probably don't hear about this with Kahrs because they are purchased in far smaller numbers than Glock and the average Kahr is probably shot a lot less than the average Glock.
Jim's Rules of Carry: 1. Any gun is better than no gun. 2. A gun that is reliable is better than a gun that is not. 3. A hole in the right place is better than a hole in the wrong place. 4. A bigger hole is a better hole.
no guns = might makes right