An open discussion for safe cracking. I'm talking home safes. 80-200 pound safes.
You have a try out combination. This is a default combo that is per programmed in the safe so the owner can set his own. If you can get the make and model of the safe you could possibly override the current combo.
Drilling
Is by far one of the most successful methods and is (I think) the way most locksmiths get into vaults. If you can get some diagrams for areas that can be drilled on the safe this would help significantly. These are known as drill point blueprints. By drilling on the axis of the lock or on the clinch of the bolt mechanism you can by pass the lock.
Something to watch out for is a glass sheet that lays in the door of the safe, it has a name but I don't recall it. But if the safe is tampered with, and the glass breaks the vault will become permanently locked. But these are only on a few high tech safes and bank vaults. Common ways to bypass this is make entry from the rear (pun) or the top of the vault.
Explosives I wont get much into because I'm not very familiar with them. If you do some research on jam shots these are strategically places bombs that blow the vault door while preserving the insides. This can sometimes be done by drilling the top, filling with water to pressurize the insides and drop a favored explosive inside. Causing the water to absorb the shock wave and push out on the door. Preserving the insides.
Air Arc Cutting
I have some experience in welding, but with the precision and control of an air arc welder I believe its possible cut out the lock dial and open the safe without damaging the insides. Altho I haven't heard of this being used I think this is a very plausible method.
Liquid Nitrogen
Very unlikely that you would have any of this, but it has been done. Applying amounts of this substances on areas of the metal will make it loose its elasticity, becoming brittle. After -200F the steel or metal can be broke with sledgehammer
Comments
Another, more faggoty example
Depending on the lock, hotwiring?
Each disk inside the safe has a notch cut out of it for the locking bar to slip in, when all the notches line up with the bar, the bar falls into place and allows the safe to open. The notch missing from each disk will make this side of the disk ever so slightly lighter than the complete side and when subjected to heavy vibrations, the disks will move and come to rest with the most amount of metal on the bottom, leaving the notches lined up at the top.
This of course will only work on safes where the locking bar is directly above the disks (which apparently is common on older safes).
If you are able to move the safe and know where about the locking bar is on that particular model, you could rotate it so that the locking bar is above the dials.
This method (which i have never tried I may add) suposidly works on some old safes, but modern safes are generally more advanced and will not be vunerable to this attack.