US NAVY/SEAL/SPECWAR model QD m203 front sight. This knight's manufactured mounting system has a mil-spec m203 leaf sight attatched, and is made specifically to attatch to rail forends (RIS,RAS,SIR,etc) . With auto-tensioning lock-down knob. These are extremely hard to find. More pics at www.picturetrail.com under user kavik1. Also look at www.specwargear.com under "specials" section. $250 shipped
Trades with compact acogs, ta 31, or ras II considered.