I own a Sig 551 and I have this on my gun
http://www.airsoftparts.ca/store2/in...oducts_id=1171
This is not my gun but it shows the rail installed.
http://i252.photobucket.com/albums/h...Picture010.jpg
Edit: check out this thread if you like the sig
http://www.airsoftcanada.com/showthread.php?t=61850 there are lots of things available for the Sig you just need to look
