As explained in The Preamble to The Bill of Rights: “in order to prevent misconstruction or abuse of its [government] powers”.
“A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.”
Before I get into cartridge cases proper, you should have an idea of what headspace is. Headspace is the gap between the back of a fully seated cartridge case and the front of the closed bolt. Headspace is measured in thousandth’s (.001)of inches. As mentioned in other articles here, if headspace gets too great, you will have bulged cartridge cases, misfires or blown out cartridge cases. The latter being scary and dangerous.
As you will soon learn, guns maintain headspace in a variety of ways. Some headspace is a function of the cartridge rim, while others are controlled by the shoulder of a bottleneck cartridge. However headspace is designed to be maintained in any particular gun, it is normal to have increasing headspace as the gun wears under use. Every gun has a tolerance level of headspace with which it will operate safely; and a level where it is no longer a safe operating firearm. A qualified gunsmith should check headspace whenever your gun is in for adjustments and/or repair. Too much is a bad thing.
There are 5 general types of cartridges/rim setups. Each is described below:
Rimmed
Semi-rimmed
Rimless
Rebated
Belted magnum
Cartridge designations used to have meaning. Older cartridges were expressed in multiple numbers i.e 45-70. This meant that the particular cartridge was 45 caliber loaded with 70 grains of black powder. A 32-30 was a 32 caliber with 30 grains of black powder. Unfortunately the changeover from black powder to semi-smokeless gun powder saw these designations become varied so that this is no longer an accurate designation for today’s ammunition. European designations remain somewhat accurate to this day. A 7.62 X 39 cartridge is one whose bullet diameter is 7.62 millimeters and cartridge case is 39 millimeters in length. The drawback to this system is that they do not indicate the diameter of the cartridge case which can vary widely.
Some barrels for use in 22’s, pistols and muzzleloaders are made from ordinance steel. Also called mild steel, cold rolled steel or low carbon steel, these usually thick barrels are sufficient for the lower chamber pressures produced by their standard cartridges. Higher pressure cartridges would erode this type of steel barrel quickly.
Higher pressure cartridges often use chrome-moly steel for their barrels. It is from the 41xx family of steel and is often referred to as carbon steel. An alloy of chromium and molybdenum, it has an excellent strength to weight ratio and is considerably stronger and harder than ordinance steel. These barrels have better erosion characteristics than ordinance steel and because they are heat treatable, chrome-moly is more flexible than ordinance steel.
Some guns have barrels made of stainless steel. Stainless steel is more expensive than ordinance and chrome-moly but is highly resistant to corrosion and erosion. Because of its high chromium content, stainless steel is more difficult to machine to exacting standards. The added expense for the raw material and the extra labor required to finish the metal make it cost prohibitive.
Rifling
Rifled barrels add significant stability to bullets as they travel down and out of the barrel of a firearm. Rifling is a series of high spots and low spots inside the barrel called lands and grooves respectively. The diameter of the barrel measured on the lands determines the barrels caliber. Rifling is measured as twist rate and is expressed as a ratio. A twist rate of 1:10 means that the bullet will rotate 360 degrees in 10 inches of forward travel.
The grooves are the low areas of the inside of the barrel and are cut out using several different methods. Cut rifling can be accomplished by cutting a single groove at a time. Broach cutting a barrel often cuts all grooves simultaneously. Button rifling is a process which cuts all grooves at the same time, usually in multiple passes. This method has the added benefit of surface hardening the steel as it is cut. Some barrels may be hammer forged. In hammer forging, a center drilled barrel blank is placed on a mandrel which is pre-shaped with a negative of the desired lands and grooves. The outside of the barrel is pounded or otherwise compressed under tremendous pressure. This compression heats the barrel and shapes it around the mandrel. The finished product is a barrel complete with lands and grooves.
Barrel Crown
It is critically important that a bullet exit the barrel at the same instant all the way around its base. If not, the expanding gas escaping from the barrel can tip the bullet as it exits the muzzle. This can induce wobble and greatly diminish the accuracy of the gun. For this purpose, each barrel is machined with one of four main types of crown: flat, tapered, stepped and round. A round crown affords the most protection of the muzzle should it ever contact a hard surface. A flat crown is easiest to machine perfectly flat and is often used in target guns. Unfortunately, a flat crown is also the most susceptible to damage should the muzzle be contacted by a foreign object.
Shotguns
Most shotgun barrels are smooth bore and have no rifling. They are usually formed by driving a bore sized mandrel through superheated steel. Often chokes can be fitted to the barrel to tighten the pattern produced by the shot. Chokes come in four designations. Full (4/4) choke offers the highest level of constriction resulting in the tightest shot pattern. Other designations are all relative to full choke and include improved modified (3/4), modified (1/2) and improved cylinder (1/4) which offers ¼ of the restriction of a full choke. Using no choke is often referred to as cylinder.
Two of the most common types of long gun stocks are the pistol grip stock and the straight stock. The actual pistol grip portion is the downturned section just behind the trigger guard. Some pistol grips have a swell on one side designed to better fit the palm of your hand sometimes referred to as a rolled hammer swell. The lower end of the downturned pistol grip is the grip cap. A straight stock as you may have guessed has no downturned area behind the trigger guard. Some stocks have a gracefully crafted and curved lower edge; this is known as a fish belly stock.
A thumb hole stock has a hole in the stock at the rear of the pistol grip to allow your thumb to wrap around the pistol grip. Often these stocks are of a laminated design. Laminated stocks are made of layers of wood glued together to create a single piece. If the layers are of different colors, these will show dramatically as the wood is shaped into a completed stock.
Beginning at the front of the gun, the section in front of the receiver or action is the fore end. A thin fore end is referred to as a splinter fore end, while a particularly wide version with a virtually flat bottom is called a beaver tail fore end.
At the Top of the stock just behind the action is the comb. This is the area where the thumb would go to activate safeties or levers, or to pull back hammers and such. Some combs have carved inlets for comfort. These molded areas are referred to as comb flutes.
The upper rear extremity of the stock is called the heel. The lower rearward extremity is the toe. The butt plate or recoil pad runs the length from heel to toe.
A cheek piece is a protrusion typically on the left side of the stock intended to give a solid cheek weld. American cheek pieces tend to be on the larger side when compared to many European models. A rollover cheek piece actually extends over the comb of the stock and ends on the right side of a right handed stock.
If the top rearward section of the stock has a carved area a few inches in length ending at the heel, the notch area is called a Monte Carlo.
A stock may have cast on or cast off. Cast off is when the centerline of the stock is to the right of the center line of the barrel from a shooter’s position. Cast on then would be a stock whose centerline is to the left of the barrel centerline as viewed from the shooter’s position.
A stock may also have either toe in or toe out. Toe in is when the toe of the stock is wider to the left side of the stock as viewed from the shooter’s position. This allows the gun to be tucked deeper into the shoulder more for stability. Toe out may be desirable in some instances such as a female shooter or a particularly large shooter so the recoil won’t pinch sensitive areas of the body.
Pitch refers to the angle that the gun tilts when rested on its butt plate or recoil pad. Pitch away is generally preferred by larger shooters. This is when the gun leans toward its bottom when rested on the butt plate. Many mass produced guns are simply neutral meaning that the gun would be square when rested on its butt plate.
Length of pull is measured from the center of the recoil pad to the center of the trigger. It can be adjusted by a qualified gunsmith by either modifying the stock or replacing and refitting a new recoil pad.
Revolvers come in two main varieties, fixed cylinder and swing cylinder. As the name implies, a fixed cylinder revolver holds the cylinder fixed in the frame. It is loaded and unloaded through the gate which swings open and allows access to a single chamber at a time. A swing cylinder swings open on its crane or yoke, typically right to left, to allow access to all of the chambers at one time for loading and unloading. The swing cylinder is latched in place by the thumb piece which is typically on the left side of the frame and is activated by either pushing forward or pulling rearward.
There are also different types of fire control actions which include single action and double action. With a single action revolver, the hammer must be cocked manually before each shot. Pulling the trigger without cocking the hammer will not operate the gun. In a double action revolver, pulling the trigger will both cock the gun and fire it in one motion. Manually cocking the hammer will allow it to be operated in the single action manner. There are some revolvers which are double action only. Many of these guns typically do not have an exposed hammer so manual cocking is not an option. While others do have an exposed hammer, they will not stay in the cocked position when pulled back.
The cylinder has multiple individual chambers. The number of chambers will vary depending on the cartridge size and frame size. Each chamber will hold a round to be fired in succession as the cylinder rotates. In the center of the cylinder’s rear face are the ratchet pads. These are activated by the gun’s hand to rotate the cylinder and index the next round.
Around the outside of the cylinder are small indentations called cylinder notches. There is a cylinder notch for each chamber. The bolt or cylinder stop locks into these notches to hold the indexed cartridge in place until fired.
In a revolver, the trigger is often also the sear and engages the hammer notches. A sear holds the hammer back until the trigger is pulled.
The grip frame is a one piece unit where the grips mount. It also functions to contain and tension the mainspring. The mainspring, sometimes called a hammer spring, gives the hammer the energy needed to fire the gun. Some guns use two individual parts to form the grip frame and these parts are typically called the trigger guard and back strap.
Your gun’s locking system holds the cartridge locked in place while the round is fired. Excessive wear or a poor fit can create excessive headspace whose symptoms may include a bulged cartridge case, a pierced primer or a ruptured cartridge case. When it fails, the locking system opens before the bullet has left the barrel and the burning gasses and powder escape through any space available. This can leave the shooter and bystanders burned, deaf and/or blind. Your locking system can be checked and if necessary repaired by a qualified gunsmith long before there are noticeable symptoms or problems.
Typical Locking Systems
• Falling Block – The breech bolt drops straight down allowing access to the chamber.
• Rolling Block – Pivots on a pin and swings open and closed. The hammer and block fit together in such a way that they hold the block closed while a cartridge is being fired.
• Rotating Bolt – Locking lugs, front or rear, are rotated into a supported area of the receiver to resist the pounding and pressure created by the fired cartridge.
• Straight Blowback – Not a literal locking system. Relies on the mass of the bolt and in most cases a return spring to retard the opening of the bolt.
• Toggle Lock – Uses two links with three pivot points to create a nearly straight line with the chamber when closed. This near linear configuration resists opening until the cartridge has been fired.
Pivot Barrel Shotgun Locking Systems
• Purdy Triple Bolting – Uses two large lugs below the barrel(s) and an additional catch high on the receiver which is operated by the lever.
Handgun Locking Systems
Whatever method of locking that your firearm uses, it absolutely must be operational for the gun to be considered safe. It is easy to just take your gun to the range, hit some targets and go home. It is responsible to pick up your spent brass and look at it. Any sign of shiny spots, bulges or anything which may appear out of the ordinary is an indication to have your gun checked. As a responsible gun owner, it is imperative that you keep your gun in good working order. Your local gunsmith can help keep you and your family safe.
G-Tech Firearms 