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Shotgun Forcing Cones

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The forcing cone in a shotgun barrel forces the shot charge or shot column down in diameter in transition from the shotgun chamber to enter the bore and then to enter the parallel section of the choke. The one we will concern ourselves with here is the chamber to bore forcing cone the other is contained within the choke or choke tube.

Short Factory Chamber To Bore Forcing Cone:

Lengthened Chamber To Bore Forcing Cone:

There has been a lot written on the subject of chamber to bore forcing cones, some good, some bad. The most experienced and authoritative goes to the late Ralph T. Walker. This appears to have been his life work. His book Gun Digest Book of Shotgun Gunsmithing is highly recommended to all who want the maximum from their shotguns. This is where I started my research as a gunsmith seeking out the ultimate in shot patterns, and it is here where the issue of forcing cones came into light for me.

Chamber forcing cones vary in length from 1/2″ to 2-1/2″ with many saying that this length or that length is perfect.

This is what I found after many hours at the lathe, chronograph, and patterning boards–1-1/2″ length will give you the best shot pattern performance, but, there is a catch to this and one that I did not see in any writings anywhere that really addressed this one issue: it is the amount of finish that you put on that 1-1/2″ forcing cone.

This is the one thing that makes or breaks successful shot pattern gains in lengthening a forcing cone, if the forcing cone is cut with a reamer of high quality the shot pattern may actually decrease if not honed some to remove the reamer ridges, if you proceed to hone the ridges then a pattern increase will start to come forward. The more you smooth out this area the more the pattern increases.

Most Important:

The end result to this is simple, cut with a reamer the forcing cone length to 1-1/2 inches, hone, polish the forcing cone, then when it is glass smooth, burnish it. This will seal the metal and a substantial gain in pattern density and evenness will be yours.

Can a longer forcing cone reduce recoil?

Simply put, the law of physics says for every action there is an opposite reaction. In a shotgun, you detonate powder which creates expanding gases that push to escape. In other words if you are pushing an object that weighs 1 ounce at a given velocity of say 1,200 feet per second in one direction the push factor in the opposite direction is exactly the same.

Felt recoil can be adjusted to give different effects by altering time frames to reach a given high point in recoil and by doing so you get more of a push effect than a punch effect at your shoulder.

Once a powder charge is ignited, it starts to push. In a barrel with a short forcing cone, the shot column that has to move is met with resistance from a steep, angled forcing cone trying to squeeze the shot column down to fit in the bore. Therefore, more pressure is needed to start moving it.

With a long forcing cone the shot column will instantly start moving freely into the bore requiring less force to move it because it is met with less resistance. As you can visualize here we just altered the time frame for the felt recoil from a punch to a push.

In both cases the shot column will accelerate until all powder is burned, giving us a desired amount of power from the expanding gases.

Can a longer forcing cone increase pattern density?

Simply put, yes. The reason that longer forcing cones give increased pattern density is that less pellets are being crushed at the back of the shot column. The reason for this is simple–the pellets in the back of the shot column have two forces working against them.

The expanding gases are trying to push them forward and the weight of all the pellets in the shot column are acting as a wall preventing them from moving forward.

In a short forcing cone the push to start moving all pellets forward is a sudden burst of pressure and the longer forcing cone allows the pellets to enter the bore in a slower push with less pressure thus not crushing the pellets and keeping more of the pellets in the pattern due to a lack of flier pellets with flat spots on them.

13 Gunsmith Schools

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gunsmith schools

Gunsmithing Schools:

—American Gunsmith Institute
American Gunsmithing Institute offers many different video courses on how to repair, clean, and customize many different types of firearms!

American Gunsmithing Institute
1325 Imola AvenueWest, Suite 504, Napa, CA 94559

–Ashworth College
Ashworth College offers a Gunsmithing Diploma with the instruction taking place online. The college gives students up to a year to finish the course, that is learned at the student’s own pace.

—Colorado School of Trades
The Colorado School of Trades prepares their students for an exciting career as a Gunsmith, operating lathes and mills, and performing detailed wood shaping and finishing.

Colorado School of Trades
1575 Hoyt Street Lakewood, CO 80215

–Marshalltown Community College
Based in Iowa, this school offers a Gunsmith Technology program on campus in a high tech environment that Brownells helped inspire.

3700 South Center Street
Marshalltown, Iowa 50158

–Montgomery community college
Students are taught skills in machine shop, metal finishing, stock making and finishing, firearm servicing, repair and the laws and regulations governing firearms and businesses.

MONTGOMERY COMMUNITY COLLEGE
1011 Page Street Troy, NC 27371
Telephone: (910) 576-6222, Ext. 264 or 1-800-839-6222

—Modern Gun School
Learn Gunsmithing in your spare time and at your own pace! Modern has trained over 50,000 students at home since 1946 in the precision craft of gun repair. We offer two levels of training: Basic Gun Repair and Advanced Gun Repair.

MODERN GUN SCHOOL
80 North Main Street, PO Box 846,
St. Albans, Vermont 05478
Phone: 1-800-493-4114

–Murray State College
Murray State is an NRA affiliated school. Based in Oklahoma, they teach everything from stock fitting to metal working and everything else in between.

Murray State College
One Murray Campus
Tishomingo, OK 73460

–Penn Foster Gunsmith School
You can get a diploma in gunsmithing in this at your own pace distance gunsmithing school.

–Pennsylvania gunsmith school
As a student at the Pennsylvania Gunsmith School you will be taught bluing, welding, chambering, lathe operation, repairing, milling machine, checkering, tool making, hand loading, forging and heat treating.

Pennsylvania Gunsmith School
812, Ohio River Boulevard, Avalon,
Pittsburgh, Pennsylvania 15202
Phone: (412) 766-1812 or Fax: (412) 766-1812

—Piedmont Community College
Piedmont offers a gunsmithing diploma that’s a great start to a career.

Person County Campus
1715 College Drive
Roxboro, NC 27573
(336) 599-1181

–Pine Technical and Community College
Pine offers a gunsmithing program on sight, located in Minnesota.

900 Fourth St. SE
Pine City, MN 55063

–Trinidad State
Trinidad State in Colorado is an affiliated with the NRA and offers a few different gunsmith programs to choose from.

Trinidad Campus
600 Prospect St
Trinidad, CO 81082
1.800.621.TSJC
719.846.5011

–Yavapai College
Yavapai college is based in Arizona and has a few different programs to choose from including a certificate, advanced certificate, and AAS in Gunsmithing.

1100 E Sheldon St
Prescott, AZ 86301
P: (928) 445-7300

*Disclaimer* We have not use most of the schools on this list, so make sure you do your due diligence before enrolling. If we don’t have your school on this list please be sure to tell us so we can add it.

Learn how to mount a scope on a rifle.

Shotgun Bore Polishing

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Shotgun Bore Burnishing:

Actual gains in pattern density, evenness and point of impact consistency can be had cheaply by simply burnishing the shotguns bore, chamber and forcing cone. This applies to all shotgun bores other than chromed bores, all shotgun bores are polished but not burnished, burnishing removes all the scratches from shotgun bores left by polishing with abrasives.

This is very consistent and your first line of defense in greatly reducing moisture trapped in the bore of the shotgun which then starts the process of rust formation in the barrel.

Shotgun bore burnishing actually closes the pores in the gun metal and leaves the metal surface very slick, it will make almost any shotgun more consistent in patterning and point of impact.

Shotgun bore burnishing reduces substantially plastic fouling left in shotgun bores from plastic wads, which in turn reduces pattern consistency.

Burnishing is really simple to do, but, it is very time consuming, when done properly, it can be very rewarding in benefit of increased pattern density and consistency.

To Burnish A Shotgun Bore All You Need Is:

1. A 3/8″ or larger dowel rod the length of the shotgun barrel.

2. An electric drill.

3. 0000 steel wool.

Note: Steel wool coarser than 000 may actually scratch the bore.

How To Burnish:

1. Take the dowel rod and make a few nicks in the end that you will run through the bore just enough to grab the steel wool.

2. Wind the steel wool around the dowel rod like a q-tip just enough so that it will pass through the bore of barrel while being spun by the drill.

3. Next just chuck the rod in the drill and start burnishing.

4. Run the whole rod back and forth the entire bore for about an hour.

Note: The barrel will heat up during this process, so, care should be taken here.

Tip: If the shotguns bore is rough from rust, a little shot of wd-40 on the steel wool will help in removing it.

Result: I have used this method on all my shotguns and results are always the same, extremely bright bores and consistent shooters.

Shotgun Barrel Back Boring

Shotgun barrel back-boring is nothing more than the machining process of reaming or boring a shotgun barrel to a larger interior diameter.

This is usually done by a very knowledgeable gunsmith in the efforts to save a rusted shotgun barrel and usually is done as a few thousandths of an inch clean up pass through the barrel.

The barrel is then usually polished and burnished inside, restoring the barrels interior back to a usable state of condition do to boring. A back-bored shotgun barrel simply means that the bore has been altered to a larger inside diameter.

Back-boring of any particular gauge, does; beyond any doubt, add to more wider center mass and will help reduce the length of shot strings in shotguns and when done within reason it does not decrease the velocity of the shotshell load.

The reason that it does not decrease the velocity is, today’s plastic wads will expand a great deal to seal the bore of the shotgun and not allow gas to escape around the wad. No gas leak, no velocity lost.

As you open up the bore of a shotgun it takes less choke constriction to still get the same pattern as one with a standard bore. This is a big bonus to all that love to shoot trap and other sporting clay games because this puts more pellets into the center mass of the shot-string and over-all shortens the shot string reducing the time frame from first pellet strike to the last.

Choke constriction is measured in thousands of an inch plus or minus from the bore diameter to a designated choke size such as 12 gauge bore .729 full choke= .035″ constriction, modified choke – .019″ constriction or improved cylinder choke = .009″ constriction. Open up the bore then you open up the choke for the same choke result on a fixed choke shotgun.

If you do decide to do this. Make sure you send your barrel to someone that is experienced with this procedure and their level of finish work is excellent. This is by no means an easy process to get right. See diagram below for other issues to consider.

Read our in depth shotgun guide, next.

Rifle Recoil Calculator

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Centerfire Rifle Cartridge Reloading Energy Calculations:

Rifle recoil and bullet energy, is a byproduct of the propulsion force generated by the powder charge held within a metallic rifle cartridge. The physical event of recoil energy occurs when a powder charge is detonated within a rifle barrel, resulting in the conversion of chemical energy held within the powder charge into thermodynamic energy.

This energy is then transferred to the base of the bullet and to the rear of the cartridge or breech, propelling the firearm rearward into the rifle shooter while the rifle bullet is propelled forward down the rifle barrel until it exits out the muzzle.

The forward moving bullet energy can be calculated easily,
simple formula; velocity x velocity x bullet weight = ?;
divided by 450,340 = bullet kinetic energy in foot pounds.

The rearward rifle energy can be calculated easily as well, which is free recoil and designated as foot pounds of recoil energy.

Recoil Fact:

Simply put the law of physics says for every action there is an equal and opposite reaction. In light of that fact it is more than fair to say that all bullets of equal weight and velocity should recoil the same.

However, there is an acceleration time frame chemically engineered into all reloading powders that cannot be ignored either and that acceleration time frame equates into what a shooter feels on his shoulder or felt recoil. Did you achieve full acceleration of bullet to peak velocity in 6″ of rifle barrel or 26″ of rifle barrel as this equates into the recoil factor.

Rifle Recoil Calculator:

Everyone that handloads rifle cartridges for their rifles is always faced with the problem of wondering how much recoil will be produced by their individual rifle from their handloaded ammunition.

Here is a rifle recoil calculator formula that will get you close to your own pet rifle load recoil if not exact. This method of calculating recoil is based on the energy of the powder used and not velocity, also beings not all powders possess the same chemical kinetic energy this formula will not be 100% but it will be very, very close.

Also you will note that when using this formula you will find that even though you will have velocity levels the same between handloads it will reflect that there is a difference in actual recoil between them.

Step 1: Add the weight of your powder and bullet together expressed in grains.
Step 2: Now multiply this number by the weight of the powder.
Step 3: Now take the weight of the rifle in pounds and decimal fraction of pounds and multiply that number by 80.
Step 4: Now divide the number you got in Step 2 by the number you got in Step 3. The answer will be foot pounds of recoil energy.

Shotgun Stock Fitting

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shotgun stock

Shotgun Stock Fit:

Getting the right fit on a shotgun stock is one of the most important things that you can do to improve your shooting and this is the one thing that most people will ignore. When you really think about it if you belong to a club with a lot of members or hunt with several different friends just look at the difference in their sizes and remember this, shotgun manufacturers have to build one stock for a given model number to fit all these same people.

Does it not stand to reason that a shotgun stock will not fit all these different sized people. Below are some adjustments that you can do yourself beyond that you really need to get a stock fitted to you by a very experienced gunsmith.

Does It Fit:
Here is a simple test to give yourself to see if your shotgun stock fits you. Make up a target approximately 2 feet x 2 feet or 4 sq.ft., place it down range 200 yards relax a few minutes, now pick up your shotgun and snap point your shotgun at the target as if it were a grouse or clay bird trying to get out of range. Repeat this procedure 4 or 5 times, now if you had to make any adjustment whatsoever to get on that target, simply put, your shotgun stock DOES NOT FIT YOU.

A Better System:
This was a system that I tried about 1978 to help solve fitting problems on people that had various health issues that prevented them from using better shooting form, what I noticed that these people were able to shoot many times better than the average person that was fitted with a stock that had been done with, by the book measurements. I then adopted this method and blended it with the book tech measurement method.

A Common Problem:
One of the biggest problems with stocks made today is the comb of the stock is really high and people have to scrunch down into these stocks to get on target. While at first you may think a lot of wood has to be removed to correct this generally not, you can sand this area down by hand and keep checking this for fit until it is very comfortable to shoot, a telltale sign of this problem is you keep getting smacked on the cheekbone with the stock.

Shotgun Stock Pitch:
Shotgun stock pitch is the angle at which the shotgun buttstock fits to your shoulder. This is very easy to detect if you have improper fit. When you fire the shotgun if it flips the muzzle up or down the pitch is wrong. With the proper pitch the shotgun will recoil straight back into your shoulder.

Shortening A Stock:
If you feel that you need to shorten your stock never cut off more than a quarter of an inch at a time until you put it all together and check it for fit. This may take more time to get to that perfect fit but its better than trying to lengthen a stock after being cut to short.
To properly cut a stock to keep it from splintering is quite simple:
1. Make a pencil mark around the stock where you want to cut it.
2. Now take a sharp utility knife and cut into the wood all the way around your stock, on your pencil mark.
3. Using a saw of fine kerf cut the stock at the edge of where you ran the utility knife, this method produces a clean cut with no splinters.

Lengthening A Stock:
While not the most appeasing look, you can buy plastic butt plate spacers black or white from brownells gunsmith supply and add these ahead of the butt plate or recoil pad. If you still need more length try adding a slip on recoil pad.