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An Introduction to Shotguns

An Introduction to Shotguns

By Numrich Gun Parts Corporation, Posted in Shotgun
March 06, 2018

Got a new shooter in the family? Have some unanswered questions about shotgun ammo? Then this just may be the article for you. This is a brief introduction to some specific points regarding shotgun shooting. So before you head out to the range with your youngster, or run out and buy them that shiny new Mossberg 500 or Remington 870, pull up a chair and review this information with them. They just may be a bit more informed and better prepared when you begin your hands-on instruction. Who knows? You might even find some of the information helpful yourself.

First let's explain what distinguishes a shotgun from other firearms. Most other guns will fire a single projectile. A shotgun is designed for shooting multiple projectiles in varying sizes and quantities. The multiple projectiles are called shot. The shot is encased in the shotshell along with the powder charge, wad separator, brass head and primer. When the shot is fired, the group of projectiles will spread out as they travel away from the gun’s muzzle. This spreading of the projectiles is called the shot pattern. There is just one exception to multi-projectile shot, which is called the slug. The slug is a single heavier projectile meant for hunting larger game. There are variations of slugs, but all are single projectile.

Shotgun Ammunition

The three general types of ammunition used in a shotgun are:

BIRDSHOT

This is the most widely used ammunition due to its broad spectrum of applications. The size of birdshot is indicated by a number. The larger the number, the smaller the projectile (or pellets) will be. Though the projectile is smaller, there will be a larger quantity of them inside the shell. The exact amount of pellets will vary by the weight of the shot.

For example a 1 oz #4 birdshot will contain fewer projectile pellets than the 1 oz #9 birdshot. The #4 pellets will measure about .24”, but the pellets in a #9 shell will be considerably smaller measuring around .08” in diameter. We have provided a chart below that will provide a more detailed reference to the size and amount of shot in each size shell.

Most boxes of shotgun shells will be clearly marked with the size and weight, and should also include their intended usage (eg: target, pheasant, turkey, etc.) Also be sure to purchase shells that are made for the chamber size that is stamped on your barrel or receiver (eg: 2-3/4”, 3”). Shells shorter than the chamber size may be used, but a shell longer than your chamber will not work.

BUCKSHOT

There will be considerably fewer projectiles inside the shell, but they are much larger and heavier than those used in birdshot. Usually these pellets will measure anywhere from .32” to .36” in diameter. Much like the slug, these bigger projectiles are meant for use on larger game (where permitted by law). The increased mass will produce more kinetic energy, however with fewer projectiles it will leave less room for error when placing the shot on target.

SLUG

A single projectile typically with a cylinder shape, but as mentioned earlier there are variations. In a comparison of 12-gauge and 20-gauge foster type slugs we found that the 12-gauge measured .678” in diameter and weighed .9 oz. The 20-gauge slug measured about .565” in diameter and weighed approximately .7 oz.

Shotshell Chart

Choke

The choke refers to a reduction of the inside diameter of the barrel at the muzzle. Some shotgun barrels will have a fixed choke, which should be marked on the barrel, and others will accept choke tubes that can be changed for different usage.

Now if you’re familiar with this blog you already know to expect at least a short history lesson. So here it goes.

Shotguns or Scatterguns as they were earlier known have been around since the 17th century and have been referred to by several different names. They are believed to be first invented in Germany and were called the Blunderbuss. These were flintlock guns that had very large bores and flared muzzles. The assumption with the design was that the flared muzzle helped control the shot when it left the barrel, but this was later proven to be incorrect. It was actually quite the opposite. The Blunderbuss had a very limited range without any real control of the shot. However, it was popular for protection and served its purpose in that regard if the target was close enough. The Blunderbusses were even known to sometimes be loaded with metal fragments or gravel if lead balls were not readily available.

Since shotgun style weapons remained popular, builders maintained their focus on evolving them and their ammunition through the years. In 18th century Britain, hunters first used what we refer to today as birdshot. Because the primary use of their guns was for pursuing large migrating birds, they were often referred to as a Fowling Piece. The term shotgun didn’t grow in popularity until around 1776 due to the need to distinguish the smooth bore guns from the rifled muskets. This term is said to have originated in what is now known as the state of Kentucky.

In the next century, firearm designers began to really experiment with the idea of actually controlling the shot. The exact point that the first choke restriction was used is up for some debate, but the first use that gained wide attention happened in the 1870’s. An inventor named W.W. Greener devised a design that allowed a barrel to be smoothly sloped to provide the muzzle restriction as the shot left the barrel. His idea was patented in 1874 and though many other shotgun manufacturers disputed his claims of better accuracy and control of the shot, his guns proved themselves in open public trials in 1875. His restricted barrels would go on to win the London gun trials in 1877 and again in 1879, and also the trials held in Chicago that same year.

Soon after many gun designers and manufacturers would follow suit and create a choice of restricted barrels. The benefit of restricting the muzzle to control the shot groupings became obvious. Yet the first successful removable choke tube system would still not appear until 1969 when Winchester introduced their Win-Choke system. A decade later Mossberg would present the Accu-Choke system and by the nineteen-eighties the removable choke was widely used throughout the industry.

The most common standard choke sizes used today are as follows:

Cylinder – Degree of restriction is zero

Skeet – Degree of restriction is .005”

Improved Cylinder – Degree of restriction is .010”

Modified – Degree of restriction is .020”

Improved Modified – Degree of restriction is .030”

Full – Degree of restriction is .040”

Extra Full – Degree of restriction is .045”

These restrictions are standard and should be relatively the same regardless of the gauge of the shotgun. Although, some minor variation may exist by manufacturer or in smaller bore shotguns such as the 28 gauge or .410 bore.

Important note: Not all choke tubes fit all guns. Sometimes not even choke tubes from the same manufacturer and same model gun can interchange. There is also the issue of tubes meant for lead and those that can be used for steel shot. Pay close attention to these things when purchasing your aftermarket choke tubes. Placing the wrong tube in your barrel may not end well for your firearm. Three specific examples that usually cause confusion immediately come to mind. They are Remington, Browning and Beretta.

Remington models use two distinctly different choke systems. The Rem-Choke and ProBore. The way to tell these two apart is pretty simple, barrels using Rem-Chokes have recessed threads approximately 1.25" from the muzzle, and the threads for barrels using ProBore tubes will be located near the end of the muzzle.

Browning shotguns use the Invector choke tube system, but there are three types. They are the Invector, Invector-Plus, and the newer Invector DS. It’s easy to see how this can become confusing if you weren’t aware of the difference. Here is what you need to know about Invector style tubes.

All 10, 16, 28 and .410 gauge shotguns will use plain Invector choke tubes. The 12 Ga. and 20 Ga. shotguns will have choke type marked on the barrel. They are also the only gauges that will use the Invector-Plus tubes. The newer Invector DS system is currently only used in the new Citori 725 & the new Browning A5 and only with 12 & 20 gauge guns.

Beretta shotguns use two models of choke tubes. They are the Mobil and Optima choke systems. The Mobil choke barrels are only marked with the gauge of the gun. They have no other marking to indicate the choke style. The tubes themselves are marked with “PB” or “ST” and the threads will be located 1.63” from the breech end of the tube.

It’s also worthy of mentioning the Beretta sometimes uses an asterisk system (eg: *=Full, ***=Modified) to identify their choke sizes. It is probably best to do some research no matter which manufacturer you’re dealing with, so you are aware of any nuances associated with your shotgun.

Barrels using the plain Optima chokes are identified by the letters “OB” stamped next to the barrel gauge stamp. The threads on the choke will be located 2” from the breech end of the tube.

Optima-Choke Plus tubes are currently used on the Xtrema, Xtrema2 and the Silver Hawk SXS 12 gauge models and the threads will be located 1.64” from the breech end of the tube.

Finally their newest system is Optima HP is only used in some select models. The following notice is taking directly from the Beretta website: WARNING: Use of the Optima HP choke tube in an Optima firearm (without the HP designation) can cause severe damage to the choke tube and barrel when the shotgun is fired. The models to date that have been designed for use with the Optima HP choke tubes are A400 Xtreme, A400 Xplor, A400 Xcel, 690, 692, DT11, and A300 Xtrema, SV10.


Shot Pattern Testing

Pattern testing should always be done whenever you purchase a new shotgun, change your choke tubes, or use new ammunition. It is the only way you will fully understand what the shot is doing after the trigger is pulled. All shotguns are unique and the additions of variables such as choke tube and ammo selection just make them even more so.

Some folks may try to avoid this extra step and just assume that if they miss their first couple of birds from the duck blind, they can simply switch out the choke tube and try again. That method will educate you about as well as closing your eyes and firing at the sound of the quack. Both ways will provide you the same percentage of information about what your shot is doing when it leaves the barrel - zero!

The bottom line is, to really understand your chosen setup you will need to see it for yourself. I am sure there are other ways to pattern test, but I find that using a 30 inch circular target at varied distances works just about as good as you can expect.

You can purchase targets that are made for pattern testing or even with turkey heads and other game on them, but it is not necessary. A 30-inch circle drawn on a light background will do just as well. Make a vertical and a horizontal line that intersect in the center to provide you with a point to rest your front sight bead.

Now before we go any further, let's just emphasize that the point of all this is to see how your shotgun fires your shot. So don’t go through all this trouble and bring a box of target ammo. You want to test the tubes and ammo that you intend to use for game hunting. Target ammunition will pattern differently.

If you are targeting ducks, grouse, or pheasants, you’re going to be looking for a nice spread throughout the circle with probably 60 percent hitting above your center horizontal line. For ground game with a small kill zone like wild turkeys you will want a tighter cluster near your center point. Typically a modified choke will provide the spread for ducks, and a full choke will cluster the shot for turkeys.

The test shots should be fired from a rest and you should take several shots at targets located at varied distances from about 25 to 50 yards. This will provide you with a picture of what your shot is doing as it travels away from you. It will also help determine your ideal range for the ammunition and choke that you’re using. If you are going to try out different combinations, it is a good practice to mark your used targets with the distance, choke, and ammo that were used for later reference. Replace with fresh targets for each combination that you test.

Another method that you can use to determine what your pattern density should be on your 30” target, or to just help you determine what size ammo and choke tubes that you wish to try, is to do the math. Yeah it’s a lot like homework, but by doing this you will be ahead of the game. (No pun intended)

To determine the shot pattern mathematically you will need to use the Percentage of Shot on 30 Inch Target table below and the Shotshell Chart from above.

Step 1 – Figure out what you want to determine (For example; You want to know what pattern to expect from a full choke shooting a 1oz size #7 bird shot at 40 yards)

Step 2 – Determine the amount of shot that is in a 1oz size #7 shell by using the Shotshell Chart from above. For the sake of argument, we’ll assume we're using lead. Answer is 300.

Step 3 – Use the chart below to determine the percentage of shot that a full choke at 40 yards should land on your 30” target. Answer is 70%.

Step 4 – Multiply the total shot by the percentage and then divide the total by 100.

Answer:      300 x 70 =21,000  and  21,000 ÷ 100 = 210

Conclusion: If your shotgun is shooting straight with the bead fixed on the center of your target and you are using a combination of a full choke tube and 1oz #7 birdshot to hit a 30” circle at 40 yards. Then you can expect 210 pellets to land inside your circle.

Percentage of Shot on 30 Inch Target

Choke Size Restriction 20 Yards 30 Yards 40 Yards 50 Yards 60 Yards
Cylinder Bore 0" 80% 60% 40% 27% 18%
 
Skeet 0.005" 92% 72% 50% 33% 22%
 
Improved Cylinder 0.010" 100% 77% 55% 38% 25%
 
Modified 0.020" 100% 83% 60% 41% 27%
 
Improved Modified 0.030" 100% 91% 65% 46% 30%
 
Full 0.040" 100% 100% 70% 49% 32%

Choosing a Shotgun

In today’s market there is a pretty large selection of shotguns available. The beginner will have to consider a few things when choosing his or her first gun. Which gauge is best? What action to choose? Is it a proper fit?

If you are only going to purchase one shotgun that you intend to use for multiple purposes, you will likely want to choose between either a 12 or a 20 gauge. Shotshells are easy to find in various sizes and affordable for both of these gauges. Although, the 12 gauge holds a slight advantage in overall versatility due to its longer range, the 20 gauge may have the edge if felt recoil is an issue.

U.S. Shotgun Gauges

10-Gauge (.775” Bore) – Heavier guns – Large shell capacity. Primarily a goose gun. Ammunition tends to be a little more expensive and selection may be limited.

12-Gauge (.729” Bore) – All-purpose gun with a wide selection of ammunition. Most common and can be used for all types of applications. Ammunition is inexpensive.

16-Gauge (.662” Bore) – Less common but versatile size. Ammunition is not as readily available for all applications in most places.

20-Gauge (.615” Bore) – Very versatile, less recoil than the 12-gauge and ammunition is plentiful. Second best all around gauge. Ammunition is inexpensive.

28-Gauge (.550”) – Much like the 16-gauge, ammunition will be limited, but recoil is minimal, but so is its range.

.410 Bore (67 Gauge) – Smallest of the shotguns. Has limited field purpose due to low shot capacity and short range. Best for expert target shooters or home defense. Ammunition is pricey.

Actions

For many of us the price matters, so take some time and do the research. Check buyer reviews and read the shotgun forums. You may find that a lower end gun is a hidden gem, and that an expensive gun has a few hiccups. Also if you are looking for a repeater consider that although a semi-automatic may be more appealing, a pump-action may get the job done for a fraction of the cost. Here is a list of all the shotgun actions available. Picking which one is right for you is going to be a personal decision based on your own needs and which factors are the most important to you - weight, balance, rapidity, capacity, etc.  If you are anything like a large percentage of us, you’ll probably end up with more than one action and gauge once you start enjoying the sport of shooting.

  • Break Action Single Barrel
  • Break Action Side X Side Double Barrel
  • Break Action Over-Under Double Barrel
  • Pump Action
  • Semi-Automatic
  • Bolt-Action

Size and Fit

Lastly we will discuss choosing a shotgun that is the correct size for you. Comfort is important and two things we would like to focus on to help make sure that you are a relaxed shooter is finding the correct LOP (Length of Pull) and choosing a left or right-handed gun.

What is Length of Pull (LOP)? The measurement between the trigger and butt end of the stock. This can be adjusted on some guns with spacers or by adding or removing the recoil pad. In extreme cases the stock can be cut down or intentionally warped to fit the shooter. Many shotguns are now produced in youth sizes that can also work well for shorter stature adults. A professional stock fitter can help determine the shooter's correct LOP, and customize other features of the stock if needed. This is probably not necessary unless the ultimate goal is to become a serious competitive shooter. Then some additional measurements will become important as well, such as the DAC (drop at comb) and the DAH (drop at heel). You will definitely want professional assistance if fitting your shotgun to that extent.

Several methods for choosing the correct LOP can be used, but it will largely depend on the shooter’s comfort. A quick method that can provide a starting point for finding your LOP is to (1) stand with your arms straight down at your side. (2) Fold your shooting arm so that it is parallel to the ground. (3) Have someone assist in measuring from the inside of the elbow to the first joint on the shooting finger where it will bend around the trigger. This should get you fairly close to your correct LOP. But when you get in the gun store, be sure to try several shotguns and it may not be a bad idea to bring along a measuring tape, or ask for an LOP measurement on each gun you try.

Just remember that when put into action a shotgun is pointed and not aimed. So you want to be able to raise it and find your shooting position quickly and comfortably.

When shooting a shotgun you will likely not have a rear sight. Your eyes will serve this function when you quickly point the bead towards the target. For this reason, you are going to want to know more than whether you are right or left handed. Eye dominance is of the utmost importance when figuring out how you will shoot.

To find your dominant eye conduct this simple test.

Step 1 – Extend your arms out in front of you. Create a triangular shape by placing your thumbs together and touching the tips of your forefingers.

Step 2 – Keep both eyes open and center a distant object in the triangle, (eg: clock or photo on the wall)

Step 3 – Close one eye. If the eye that is open kept the object in the triangle that is the dominant eye. If not repeat the test, but close the opposite eye and the object should remain inside the triangle.

If you find that you are left-handed, but right eye dominant (or vise versa) you may want to take some time to shoot with instructor or someone more experienced before deciding on a shotgun of your own. This way you can get a feel for what works for you. Typically when it comes to shotguns, your eye is going to dominate your decision.

We hope you found this introduction to shotguns helpful. Happy shooting!