I have an 870 with the open sights slug barrel. I want to add a scope. Ive seen a saddle tactical type made from aluminum, picatinny rails. It mounts with two screws that replace the standard fire control group pins. Anyone have experience with this type mount? Also what would be an OK inexpensive variable scope. Or should I be thinking about a single power scope, this would be woods hunting only. Probably no more than 50-70 yds. Thanks. Uncrichie.