Welcome to Johnny's Shotgun Chokes and Forcing Cones...
Twenty years ago, the most requested alteration to a shotgun barrel was screw-in choke tube installation. Twenty years ago, the least (almost never) requested alteration to the shotgun barrel was lengthening of the forcing cone. This has all changed. Over the years shooters have become much more educated in this area. In the beginning most customers didn't know what the forcing cone was and didn't understand its function or what I wanted to do to it. Now days I find that a large percentage of the people who call me already know they want the forcing cone done, they are just calling for clarification and details on their particular barrel.
Twenty years ago, I was confident that lengthening the forcing cone worked but, in the beginning, most of the evidence that I had was just based on my own testing. Now, with 20 years of customer feedback from lengthening and polishing hundreds of forcing cones, the evidence is overwhelming that this forcing cone thing does work. I still make it a habit to check the forcing cone on each barrel that comes in for choke work to see if it has been lengthened. If it has not, I always mention it to the customer because not everyone is familiar with it, but this has changed drastically over the years.
Many of my new customers get my number from a friend or from someone at some type of competition like card shoots or trap and skeet clubs. My customers are my biggest promoters and I've learned a lot from them over the years. Many of them will call me to tell me how my work improved their patterns. There are guys out there that do such extensive patterning that it is almost a second hobby. These are the guys that, over the years, have helped educate me as to how my work affects their patterns, much more than I could ever learn by my own testing.
Below I will explain the forcing cone, what it does and how it can be modified to improve the performance of a shotgun.
The Mysterious Forcing Cone
The forcing cone is the constriction at the end of the chamber that forces the load down from chamber size to the size of your shotgun bore. If you hold the barrel up, point the muzzle toward the light and look through it from the chamber end, the forcing cone will appear as a short, dark ring, dark because the angle of the short forcing cone is severe and is hidden from the light. The distance from the beginning to the end is about 1/4 - 1/2", give or take. Most barrels come from the factory with this abrupt constriction, or forcing cone.
When the shotgun is fired, the shot load is immediately FORCED, under tremendous pressure, to squeeze through the abrupt forcing cone to the smaller size of the bore. The shot in the back of the load move first and they have to push the guys in front of them through that abrupt forcing cone. This results in some of the lead shot becoming deformed, making them ballistically unsound and causing them to fly out of the pattern. Lengthening the forcing cone by changing the abrupt angle to a more gentle, gradual constriction results in a new length of around 1 3/4" and a much more gentle angle of constriction. This optimum new length and less severe angle from chamber ID to bore ID allows the shot to make a more gradual transition from chamber to bore size, reducing shot deformation and allowing more of the shot to remain in the pattern.
It has been interesting over the years to watch the debates over whether lengthening the forcing cone does any good. Here is a snippet from an article in the December 02, 2012 issue of Shotgun Life magazine on the new Beretta 692:
"Steelium Pro enabled Beretta to elongate the forcing cones and eliminate the typical bottleneck in the transition from the monobloc. The longer forcing cones moderated felt recoil, muzzle jump and shot deformation, according to Beretta. Now a Steelium variant called Steelium Plus is introduced on the Beretta 692. Although it has the same metallurgical properties at Steelium Pro, the forcing cone length of 14 inches falls between the 682 (2½ inches) and DT11 (19 inches)." End Quote
Well, looks like it does work, which many of us have known for many years.
Cutting this new forcing cone is about half the job. The second half, which is often overlooked, is the polishing step. It is extremely important for many reasons, which I explain on another page called Proper Forcing Cone Polishing
Be sure that if you get your forcing cone lengthened that the polishing step is part of the deal. Guys don't like to do it because it takes so much time, but it has to be done. Please read more on polishing on the other page.