Originally Posted By: Evil_LurkerWhat's the diameter of that take-down pin?
Looks large, like the old Colts, but maybe it's the picture.
You sure it's bottoming on the shelf?
This could be a possibility - it's not bottoming out, it's just that the pin on the lower is too large for the upper. If that's the case, you would need an adapter to use the newer/smaller pins that would work with your upper receiver.
adapters to go either way-
http://www.midwayusa.com/product/316328/dpms-offset-screw-and-nut-ar-15-matte
http://www.midwayusa.com/product/599768/...vc=S015ID316328
