500 nitro - OK I did it to a matched pair of beretta golden sables too. On the 9.3 I machined the dovetails into the rib just like the merkel. On the 06 since I wasn't worried about a detachable scope I took a piece of barstock and machined 2 dovetails for the full length, then cut a slot out of the bottom so the bar would fit tightly over the rib, and is held tight by 2 set screws on each side. Gee this is a tame site, When I mentioned doing my merkel on ar I thought my ancestory had been changed to scratching myself while my parents were married.