The step down upper rail creates a thicker rail which causes the carrier to fit a little tighter. When the trigger/hammer pin holes are drilled before the receiver is bent, the trigger hole will have a slight stretch to it at the bend. I have an "economy" on order and I've only read good things about them. They will be perfect for your "beater" guns. An "authentic" builder won't use them because they have S and F selector markings. Harlan posted about the premium receivers, but I can't find it. As I remember the price will be close to his Yugo receivers. They will not have predrilled trunion holes, selector markings, or selector notches. They will have stepped rails and laser cut trigger/hammer pin holes. This way a builder can mark the selector to match the origin of the kit. Harlan watches the boards, so hopefully he will correct me if I'm wrong.