Master Locks are a great asset for securing your property. How ever forgetting your combination or loosing your keys can be a really bad thing, heres the how to on opening a master lock.
First step is to be prepared. It's not a bad Idea to keep a copy of your key or combination in a locked box or somewhere secure so no one has access but you. That way you can avoid ruining the lock or waiting to contact the manufacturer and open the lock when you need to.
Assuming that a copy of the key or combo. was not available , you can contact the manufacturer and request a key or combo. There is a Form that Master Lock requires before they will release a key or a combo. This is for security reasons and can take up to nearly 2 months.
Master Lock is a leading maker of locks currently and with good reason. You can try a hack saw to the lock rung but that will take a long time and maybe even a few blades not to mention a very tired arm. Drilling most locks that are case hardened is a joke for the same purposes, they are made of hardened steel and will dull most drill bits very fast.
I have forgot my key at work one time and I was able to use a set of industrial bolt or lock cutters. You will have to put a lot of force on those cutters to snap the steel. Torching the lock is a alternative but not every one has a cutting torch laying around. I have also had good luck with air cut off tool. The metal cutting discs cut through the steel pretty well. Again that is assuming you have access to those tools.
Breaking or cutting the lock depends also on the lock and its position. Some security locks have a guard around the lock rung making it very hard to cut. If the lock is in a recess like in some storage units or contractor grade tool boxes only the key hole is exposed and you can't even get to the rung.
If all else fails you can contact a lock smith. it will probably be expensive but they can either help you remove it or get a key made. Most lock smiths will need to see ID and have some other questions to verify your not breaking in to something that is not yours. Lock smiths may not be able to get on site right away either, so waiting might become a necessity. Lock smiths can be found in most phone books.