I think you can use the van Dale translations here (and from van Dale I now know the origin of the expression 'draw a bead on').

See also:

Sights - The aiming device on a firearm. On most rifles and handguns, the factory-installed sights consist of two elements called "front sight" and "rear sight," which together frequently are called "iron sights" because they are made up of principally metal. The front sight, located on the barrel near the muzzle, is usually post-shaped or bead-shaped and hence sometimes called post or bead. The rear sight is usually located partway down the barrel, near the breech or on the receiver. If it consists of a V- or U-shaped notch in a flat piece of metal, it is called an "open" sight. An open sight with a deep U-shaped notch with protruding wings is called a "buckhorn sight." The rear sight can also consist of an aperture in a disk. It is then called an aperture, or peep, sight. When the aperture sight is attached to the receiver it is called a "receiver sight" and when it is attached to the tang it is called a "tang sight." When the aperture adjustments have micrometer settings, such a sight is cometimes called a "micrometer sight." A hunting shotgun usually has only one sight consisting of a bead near the muzzle, but most trap and skeet guns have a second bead halfway down the barrel. There are also telescopic sights for rifles and handguns.
http://www.myoan.net/hunting/jargon.html