Looks like a Magna Ported gun. They put out special editions from time to time. At one time they were very popular. The 1980 Gun Digest has an article on Magna Ported Rugers, but the gun you show is not in there, but several that look similar.
I recall seeing an article on one of those is a gun magazine sometime back. As I recall, a custom gunsmith was turning them out. Unfortunately, I don't recall which magazine nor do I recall the name of the gunsmith. I did a search on both Guns and Ammo and Shooting Times websites but no luck.
Chances are good that I still have that magazine haning around here somewhere, if I find it, I'll let you know more.