origin of terms...and varied usages
For generations, since probably about 1911 or so, the phrase "cocked and locked" has been consistantly used for one thing, and one thing only. It refers to the 1911 style semi auto pistol. It comes from the Army name for the thumb safety, and the fact that the safety lever "locks" into position. Look it up, and you will find old GI parts manuals for the 1911 all refer to the thumb safety as the "safety lock". So "cocked and locked" refers to the 1911 (or other gun of this type) with the hammer cocked and the thumb safety "on". "Locked".
A liberal use of "cocked and locked" can include any firearm cocked with the safety engaged, but the origin of the phrase is specific to the 1911 series of guns. A GLock, for example, cannot be cocked and locked. There is no safety lever to "lock".
I never heard the phrase "and ready to rock" used that way until recently, and it certainly sounds good. To me it confers the image of mentally prepared to use the gun, the condtion of the shooter, not the gun itself.
Cocked and locked describes the gun,
ready to rock, the shooter.
Can't verify the accuracy of the Nugent quote, but it certainly sounds like something he would say.
"Lock and Load" is a range command used in the military. At least it was back in the dark ages when I was in. "Lock" refers to locking the magazine in the weapon (M14/M16/1911A1) and "Load" refers to loading the chamber. This phrase generally superceeded the old "Load and make ready". Where
load was to load rounds into the magazine, and
make ready was to chamber a round.
Many civilian ranges still use the "load and make ready" command, as it applies to everything, even BP muzzleloaders, where load is to load the barrel, and make ready to cap and/or cock the gun.
Load and Lock is a command I have never heard, and because I am familiar with Lock and Load, it sounds silly.