Maybe your not setting the pins at the shear line. Maybe you are getting the pins stuck at the shear line. When a pin stack is picked, the lower pin should fall back down into the keyway, sometimes you can actually see over the top of the pin (there will be a gap between the top of the lower pin and the plug). If you can't see over the top of the pin, then you will just have to feel for spring tension on a pin. If there is no longer spring tension on the pin then it it most likely picked. A pin stack is NOT picked when the keyways is clear of pins. This means that when you look into the keyway then wont see any keypins as you have them all stuck up at the shear line. This is NOT what you want to do. Since you are new to the "lockpicking game" I am assuming this is what you are doing.
Also, what I tell pickers new pickers:
1) USER MORE TENSIONS ON THE TENSION WRENCH while..
2) APPLYING LESS SHEAR FORCE WITH THE PICK.
3) Hold the lock in your left hand, keyway facing down.
4) Use your index finger to apply tension to the tension wrench.
5) With padlocks, always use this method of applying clockwise tension.
6) If you are left handed, do the same thing in the left hand, use you thumb instead of your index finger.
Also, just because you can pick a master lock, doesn't mean your going to be able to pick anything else. Most master locks behave in ways that are alien or opposite to how I consider locks are suppose to operate. Sometimes i get such little feedback on a masterlock that after spending all day opening 7pin tumbler ABUS locks, I cant open a master number 2 if my life depended on it. Throw all your master locks away, and then post about how amazing your master lock was on their website:
http://www.masterlock.com/apps/testimonial/stories.jsp
You can say "My masterlock was so "*hitty and easy to pick, that i threw it away after one day!"
See if they post that in their stories page
If you don't open the lock after all that, then try harder.
