My brother gave me this 586-1. It appears to be well used but well cared for. It has silhouette front sight which I imagine is not too common. Since the 586 has a full underlug, why would someone add this massive underlug weight? It is extremely heavy which, to me, would be worse that the amount of reduced muzzle flip it might prevent. No markings, but two set screws underneath. I will be removing, but am fearful of scratched bluing. Sorry, not sure why the pics are upside down.
I have a couple of those from the old days JARVIS was probably the most well known. I have a blue with no marking. The set screws leave a little indent on the bottom of the barrel lug, As long as they are kept tight , if it loosens up the weight beats around on the barrel. A few guys I have seen shoot PPC open class with that setup. Front sight set for 7-15-25-50 yard shooting. Wasn't real popular but worked.
Also, in Met. Sil. you are lying on your back with the handgun braced against the side of your leg. The underlug then becomes a positive for heavy loads.
When I competed in PPC a couple of irregulars used that set up. A dedicated PPC revolver would appear to be the ticket. My Davis revolver was rifled specifically for the 148 grain dewc.