Try using a hot towel prior to your shave just to soften up the beard as much as possible. Also, you pointed out that the razor shaved your arm hair just fine, but not your beard. I have also experienced this, so I do not believe that this method is an adequate sharpness test. This of course is my opinion, I don't speak for everyone here. Have you tried pre-shave oil? Good luck on gettin' that perfect shave!