[Yosemitest]

Watch this video, Loading and Shooting the M1 Garand.

.

This is the source for that saying.

"The second explanation is that
the phrase (as "load and lock") originated during World War II
to describe the preparations required to fire an M1 Garand rifle.
After an ammunition clip was loaded into the rifle
the bolt automatically moved forward in order to "lock" a round into the chamber."

Or ... this source.

"This imperative phrase originally referred to the operation of the M1 Garand Rifle, the standard U.S. Army rifle of WWII. Its meaning is more general now, referring to preparation for any imminent event.


The original phrase was actually reversed, "load and lock."
The phrase refers to inserting a clip of ammunition into the rifle,
"loading," and "locking" the bolt forward
thereby forcing a round into the chamber.


The phrase first appears in Gach's 1941-42 In the Army Now. It was immortalized by John Wayne (who else?) in 1949's "Sands of Iwo Jima," where the Duke reversed the phrase to the current "lock and load."

I SAY AGAIN ... Watch this video, Loading and Shooting the M1 Garand

.

[Yosemitest]

"It was immortalized by John Wayne (who else?)
in 1949's "Sands of Iwo Jima,"
where the Duke reversed the phrase to the current "lock and load." "

Having fired the M1 GARAND myself, I can understand John Wayne's reversing this saying.

BECAUSE ... you have to "LOCK" THE BOLT "BACK"
BEFORE ... you "LOAD" A FULL CLIP OF AMMO into the weapon.
Hence ... "LOCK and LOAD."