Mason moved the rear sight to the rear of the barrel as opposed to the hammer or the breechblock of the earlier efforts.
From the en.wikipedia.org
The front of the barrel was called the muzzle, and the rear was called the breech.
From the en.wikipedia.org
Releasing the lock and pushing the barrel down exposes the rear face of the cylinder.
From the en.wikipedia.org
Semi-automatic pistols have a single fixed firing chamber machined into the rear of the barrel, and a magazine, usually removable, so they can be used to fire more than one round.
From the en.wikipedia.org
Changes to the base design include a pistol grip, different type of bipod, open-type V-notch rear sight and a slightly longer barrel.
From the en.wikipedia.org
A portion of the expanding propellant gas was tapped off from the barrel, driving a piston to the rear against a spring.
From the en.wikipedia.org
The tips of the accelerator's two curving fingers engaged the bottom of the bolt and caused it to move rapidly to the rear, extracting the fired cartridge casing from the barrel.
From the en.wikipedia.org
He has to barrel through traffic on his little wheeled platform, propelling himself with his hands and hitching onto the rear bumpers of other vehicles for extra speed.
From the time.com
The M1 and M1A1 had a barrel without cooling fins, a simplified rear sight, provisions only for box magazines, and the charging handle was on the side of the receiver.