The 51668 has a rear ghost Ring sight only (No Picatinny Rail mount) and is sold only to "Qualified Professionals" LE only. The 51771 has a Picatinny rear sight rail for adding a red dot or other optic as well as a rear sight.

The 51771 has a Picatinny rear sight rail for adding a red dot or other optic as well as a rear sight. The 51668 has a rear ghost Ring sight only (No Picatinny Rail mount) and is sold only to "Qualified Professionals" LE only. (Both have the "Speed feed Stock).

Hi Michael, The only difference is that one is the LE model. In specs everything is the same except the LE model has a speedfeed stock.
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