looks like a masterlock 930 clone.
http://www.masterlock.com/cgi-bin/produ ... late=style
it may have spool pins in it. so read up on how to pick those. also have you picked anything else? this lock may be hard for a starting lock if it does in fact have spool pins.
try searching on spool pin picking and you'll find a lot of good information, along with stuff that explains how to tell if you are indeed feeling spools (the plug spins suddenly while you are picking, then stops, then when you lift a pin you feel the plug try and rotate back in the opposite direction.)
otherwise try different amounts of tension, tension from the top, the bottom, and the center of the lock to see which works best. try raking it a few times (3-4 strokes) then single pin pick the rest. or just use thermite.