My few cents worth...
I believe I can add some valuable insight to this discussion...
My father and I have always been deeply involved in the shooting sports, and he happened to be involved in the contracting of the well-remembered Master Lock commercial discussed here.
All of these 'what about X' comments are kind of missing the essence of the matter--- each of the apparently conflicting statements are true. It IS possible to kick a lock apart with your foot, AND it's possible to have bullets 'bounce off' of one... It's all a question of the energy involved, and how it's applied to the lock.
So, whatever it is you hope the lock will do, you merely have to apply the right force to cause that effect.
In the case of the Master commercial, they wanted what you saw in the final TV edit--- a nice, clean hole right through the lock, with the lock staying locked. What they actually got on the first try (using an elephant rifle with standard jacketed bullets) was a lock so completely blasted apart they couldn't even find any parts of it, excepting the shackle of the lock (which was horribly bent but still on the metal staple).
To get the effect shown on TV, they switched to a different choice of firearm and cartridge (for higher velocity), and used armor-piercing bullets (I seem to remember it was a .300 Winchester Magnum, but don't quote me on that; certainly one of the 'belted magnum' rifle calibers). This gave them the nice clean hole they were looking for, without delivering enough energy to destroy the lock.
Incidentally, there was also an inset photo in some of the print ads which 'showed' that it had taken 16 shots of this type to actually open the lock--- overall, both presentations implied that a Master padlock couldn't be shot open with a gun. In point of fact, some of the more wildcat handgun cartridges could probably do it; as long as they delivered enough energy. It has to go somewhere, after all...
In the commercial, most of that energy went right out the back of the lock, along with the bullet. On that first, lock-destroying attempt, just about every last foot-pound was delivered directly into the lock body, with predictable results.
Someone mentioned the .50 AE (Action Express) handgun cartridge-- it should be noted that this is not an excessively-powerful handgun cartridge (at 1,250 ft·lbf), not as powerful as the .454 Casull (1,923 ft·lbf), for example, and certainly nothing like the .50 BMG machine-gun cartridge. Just because they both have a diameter of .5 inches doesn't imply any other equivalence--- so that statement about "shooting down airplanes" with a .50 AE is pretty silly. The .50 BMG, on the other hand, has MORE than enough energy to destroy these locks--- as much as 14,895 ft·lbf, with an 800-grain bullet. But the .50 BMG sniper rifles weren't really around yet when that commercial was made.
Having fired an elephant rifle myself (in .470 Nitro Express), I can assure you it's an incredible amount of energy these rounds offer--- in the case of that particular caliber, 5,140 ft·lbf or 6,970 J of energy. I think it's clear, if you think about it, that this kind of energy simply MUST destroy the lock if it's effectively delivered. To turn things around a little, just consider how that kind of blunt force could be applied to a little piece of steel and NOT do significant work on it...
Just to advance the discussion...