[ibbryn]

Try this for me.
Load a revolver. Place a trigger lock on it (I know the trigger lock people say not to place the lock on a loaded gun, but humor me).
Pull the hammer back.

Now what?

[supercat]

Try this for me. Load a revolver. Place a trigger lock on it (I know the trigger lock people say not to place the lock on a loaded gun, but humor me). Pull the hammer back.

Now what?

If the revolver is loaded, odds are you now have a very dangerous situation which cannot be safely defused without being able to undo the lock (since many revolvers do not allow the action to be opened when cocked).

New England Firearms shotguns are the same way.

A slight irony is that an ordinary padlock will do a better job of securing either type of firearm, if it's placed behind the trigger, than will a "trigger lock", since it will prevent the weapon from being cocked in the first place.