Common Firearm Terminology: Definitions and Explanations. By GunsmithG
Greetings, all. As I've been writing some firearms articles lately, I've recieved a number of emails and tweets asking about certain terms I've used. I apologize that I haven't done this sooner, to help alleviate some of the confusion generated by words and abbreviations commonly used in both gun-smithing and recreational, hunting, and competition shooting sports.
I hope this will help firearms enthusiasts old and new to better understand the sometimes confusing arcana of the profession. These are not in any particular order, as I'm too lazy to alphabetize them. With that, let's begin!
Mil: A measurement first used by artillery, a mil equals 36 inches at 1,000 yards. The term has become popular since the introduction of Mil-dot reticles in rifle scopes, as you can use the size of objects compared to the dots for a range to the target, and also can be used to determine bullet drop compensation.
Scope: A common contraction for a telescopic sight. Scopes allow us to see more clearly and magnify objects at distance so a shot can be placed precisely.
Reticle: This is the term for the aiming device inside a telescopic sight, such as cross-hairs, that give you a aiming point. There are numerous different reticles in common use today, such as plain cross-hairs, duplex reticle, which uses a thicker cross-hairs, then narrows near the center, a post reticle, that usually looks like a mini obelisk, Mil-dot, usually a fine wire cross-hair with dots added to the horizontal and vertical, dot, a simple round dot in the center of the optic, and many others. You may also find dots listed as 1 mil and up, meaning the size of the dot in inches at 100 yards. One mil is equal to 4 inches at 100 yards.
MOA: An abbreviation for Minute Of Angle, meaning 1 inch at 100 yards. An example: "That rifle will shoot MOA groups". This means simply that the firearm will place a number of shots fired in a one inch group at 100 yards.
Group: A number of shots fired at a target, using the same aiming point for all. The accuracy of the firearm (and it's owner!) can be measured using this.
A flyer: A single round fired at a target that from either a movement of the shooter (a called flyer), or a shot that strays from a group for unknown reasons.
Bedding: The mating of the action and barrel of a rifle to the stock, can be inletted (carved out wood) or "glassed", the technique of using fiberglass resin to make for a solid consistent mating surface of the action to the stock to attempt to improve accuracy.
Floated, or Free Floated: The removal of material (wood or fiberglass) forward of the action under the barrel to keep the point of impact from changing as the barrel heats up from repeated firing.
Headspace: This is the critical measurement of the space between the measurement point on a cartridge to the bolt face. For rimless cartridges, the measuring point is at the mid point of the shoulder of the cartridge to the bolt face, Rimmed cartridge is measured from the rim to the bolt face, and magnum cartridges measure from the belt to the bolt face. Too much headspace, and the cartridge casings can split or separate, too little, and there may be extra high pressure in the chamber from not being able to expand properly. Very dangerous, especially in old military rifles that are badly worn.
Cartridge Casing Design and Nomenclature: The parts of any metallic cartridge are:
- Casing: The brass or steel casing that holds the powder, primer, and projectile (bullet).
- Berdan Style Primer: which is a simple cup with the priming compound in it, which usually has several flash holes leading into the powder chamber and has a part of the casing in the primer pocket that is used as the anvil.
- Boxer Primers: Use a metal cup with a crimped in anvil, and a centered single flash hole in the casing, making it much easier to reload the expended brass. Cartridge casings fall into several designs. Rimmed, where the primer end of the casing has a protruding rim around the base. semi- rimmed: A smaller, less protruding rim, the .38 Super Colt cartridge is a good example.
- Rimless: which actually have a rim, but its inset in a groove at the base of the cartridge, no larger than the cartridge base. This works especially well in semi auto firearms, and is the most common type today.
- Belted or Belted Magnum: This type casing has an extra thickness at the base of the cartridge, allowing for higher chamber pressures without the casing bulging or cracking.
Primer: a small metal cup filled with a substance that burns rapidly when physically struck, used to ignite the powder charge in the casing. There are two types of primers in common use today.
Elevation: The up and down adjustment of the bullet impact. Most all firearms have at least some adjustment in windage, as no two people see sights the same way.
Six O'clock Hold: When firing at a target, adjusting your point of impact to the center, using the clock-face as a reference point. A six o'clock hold means you place the top of your front sight at the base of the center ring on the target, with point of impact above and centered.
Maggies Drawers: A slang term from military and competition shooting. When there was a complete miss of the target, the target spotter in the pit below the target would wave a white or red flag across the target, indicating a miss.
Stripper clip: A simple sheet metal strip, with a rolled edge, that will hold a number of cartridges together in a row. Usually used to reload a military rifle with an internal magazine quickly.
Clip: A sheet metal device used to hold a number of cartridges, that becomes an integral part of the firearm till the ammunition it holds is fired. A M-1 Garand is a good example.
Magazine: a separate self contained device with a internal spring to hold and feed cartridges into the chamber of a firearm. Often referred to erroneously as a "clip".
FPS: Acronym for Feet Per Second, a common measurement of the speed of a projectile after firing.
Velocity: The speed of the bullet fired from a gun. Can be affected by heat/cold, distance, and powder charge.
Muzzle Energy: The measurement of a combination of bullet weight, and the speed of the projectile converted to foot pounds. Literally, foot pounds is the energy required to move a pound one foot.
Jam: usually encountered in semi automatic firearms, can be a casing that isn't thrown clear of the action of the weapon. Can also have a number of other causes.
Indexing: When handling a firearm, rifle or pistol, keeping your index (trigger) finger off the trigger and pointed forward along the side of the firearm.
Cook Off: This is a dangerous situation when the barrel of a firearm becomes so hot that cartridges fire without the trigger being pulled.
Squib Load: A cartridge that has either no gunpowder, or not enough to push the bullet clear of the barrel. Can be especially dangerous if another cartridge is fired, pushing both bullets through the bore, with a spike in pressure. Usually damages the firearm, at a minimum putting a "ring", a bulged spot in the barrel. In thinner barreled guns like shotguns, can blow apart the barrel.
Single Action: Can be either a semi auto or revolver, meaning that the hammer of the semi auto must be cocked for the first shot. A revolver of this type must have the hammer cocked for every shot.
Double Action: Once again, can apply to both semi auto and revolvers. The mechanism can be fired by pulling the trigger which cocks the hammer. The hammer can be manually cocked for a shorter lighter trigger pull for better accuracy.
Well, I'm going to wrap this one up for now. I'll have some more info for you all another time. Keep reading! GunsmithG
Greetings, all. Here's a little info that I've found useful. This is something I would always do, even to brand new out of the box scopes before installing on the intended firearm. Every modern rifle or pistol scope that has internal adjustments has an optical zero point, that is, where the adjustments for the point of impact are centered with the tube, giving you the most adjustment that is possible without changing the mounts themselves. Now some mounting systems, like the Redfield type, have a dovetailed front ring and setscrews on the rear ring for coarse adjustments for wind-age (side to side).
Other mounting systems, like the weaver style or picatinny rails, don't have a way to compensate for wind-age, although some scope rings may have a small amount of adjustment possible, like the Millett rings for Weaver style bases. This is why it's very important to have the scope you are going to mount as close to optical zero as possible.
Here's a simple way to check the scope for optical zero before installation. First, you'll need to make a simple cradle that can be as easy as a shoebox, or if you mount or swap a lot of scopes, a more permanent tool. I made mine from a old miter box. the design is simple, just a frame of wood, (using metal may damage the optics finish), with a V shaped cut on either side of the framework. Make sure it is wide enough to give the adjustment turrets room to rotate without the scope being moved from the V shaped notch.
The main idea being to be able to rotate the scope 360 degrees without interference from the adjustment turrets.
Set this up on a workspace where it is stable, and put a grid type target on a stand or wall that you can see clearly through the scope.
After setting the scope on the stand, move it until the cross hairs align with the center of the grid/target. Rotate the scope on its supports without lifting or shifting it, and you may see the cross-hairs or dot move away from the center of the grid. Use the internal adjustments of the scope to correct this until you can rotate the scope 360 degrees with no shift from the center of your target or grid. The scope is now at its optical center and ready to be mounted on your weapon and zeroed for point of impact. This simple system may save you a lot of grief, as it gives you a reference point and the maximum amount of internal adjustment from the scope. This is exceptionally handy when installing used optics.
Thanks for reading! GunsmithG