BELLRINGER: What do you know? How are gun barrels formed? What does “caliber” mean? How are individual guns manufacturers identified by simply looking at a fired bullet? How are fired bullets matched up to an individual gun?

Firearms Objective: Distinguish between class and individual characteristics of firearms.

“Rifling” If you “rifle through” something, what does that mean? “Rifling” in gun manufacturing is impressing the inner surface (the “bore”) of the barrel with spiral grooves. Why do you want spiral grooves?

“Rifling”, continued…. So the “valley” areas on the inner surface of the barrel are called _______, and the “raised” areas between them are called “lands”.

“Caliber” Who knew what this meant? Def.: the diameter (???) of the bore of a rifled firearm, measured between opposite lands Caliber is usually expressed in hundredths of an inch or millimeters (i.e., .22 caliber and 9 mm).

Test Your Knowledge How many lands/grooves? What is the caliber?

Identification of Gun Manufacturer Review: What are “class characteristics”? Answer: properties that can be associated ONLY with a certain group, and not an individual object The number of lands and grooves is a class characteristic.

Identification of Gun Manufacturer, continued… Each manufacturer uses a different rifling process, but each class of gun for that manufacturer has a set number of lands and grooves.

Identification of Gun Manufacturer, continued… .32 caliber S&W revolvers ALL have 5 lands and grooves twisting to the right. Colt .32-caliber revolvers have 6 lands and grooves twisting to the left.

Individual Characteristics What does this mean? Can be used to identify individual guns within a class.

“Striations” Def.: stripes or fine lines etched into the interior of the barrel These are impressions of small imperfections on the rifling tool or are produced by tiny chips of steel pushed along the barrel by the cutter. NO TWO RIFLED BARRELS HAVE IDENTICAL STRIATION MARKINGS!

Striations

Shotguns Classes of shotguns are identified as “gauges”. What does the “gauge” of a shotgun tell us? The higher the gauge number, the smaller the barrel.

Shotguns, continued….. Originally, the gauge number told you how many lead balls with the same diameter as the barrel would weigh a pound. Exception to the rule: .410 shotgun has a .14-inch bore. Can this same individual identification process be used for both handguns and shotguns?