I'm sure some people disagree with me and will not hesitate to say so, but there aren't any dumb questions out there. No one can know everything about every subject (unless its me explaining things to my wife!) so ask away! 
The difference is that the original AK spec - milled receiver - had a certain size of rail @ 1.6mm (as I recall). The transition to the AKM with a stamped receiver @ 1mm meant enough slop on the carrier that it causes feed issues, etc.
Stepped rails simply add a "notch" or step to the rail to make it take up the slack in the grooves on the carrier. Some build designs such as the Yugo M70 used a 1.6mm stamped receiver and don't need those steps as a result.
That's also the reason you have the X and Y dimples on a stamped receiver, so the pins etc. will fit without the slop.
If you think about it, a great deal of the feed issues that home builders encounter is due to the fact that the parts are built for 1.6mm thicknesses and we are using 1mm home built receivers WITHOUT these things like stepped rails, X-Y dimples, etc. etc. We usually live with the slop, but the most ideal solution is to incorporate steps, dimples, etc. into the build so we can be sure that everything works as it was designed.
The difference is that the original AK spec - milled receiver - had a certain size of rail @ 1.6mm (as I recall). The transition to the AKM with a stamped receiver @ 1mm meant enough slop on the carrier that it causes feed issues, etc.
Stepped rails simply add a "notch" or step to the rail to make it take up the slack in the grooves on the carrier. Some build designs such as the Yugo M70 used a 1.6mm stamped receiver and don't need those steps as a result.
That's also the reason you have the X and Y dimples on a stamped receiver, so the pins etc. will fit without the slop.
If you think about it, a great deal of the feed issues that home builders encounter is due to the fact that the parts are built for 1.6mm thicknesses and we are using 1mm home built receivers WITHOUT these things like stepped rails, X-Y dimples, etc. etc. We usually live with the slop, but the most ideal solution is to incorporate steps, dimples, etc. into the build so we can be sure that everything works as it was designed.
