Welcome to Johnny's Shotgun Chokes and Forcing Cones...
In my experience in shotgun work, dealing with average customers who are looking for an improvement to their favorite old smoke pole, the screw-in choke tube is the most requested alteration. The least (almost never) requested alteration to the shotgun barrel is the lengthening of the forcing cone. I make it a habit to check the forcing cone on each barrel that comes in to see if it has been lengthened. If not, I always mention to the customer the advantages of lengthening the forcing cone. In the majority of cases, the customer doesn't know what the forcing cone is or doesn't understand its function. Here we will explain the forcing cone, what it does and how it can be modified to improve the performance of the 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". 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. 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". This optimum new length 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. The combination of the screw-in choke tube and the long forcing cone can turn an old shotgun into a much better performer with considerable improvement in pattern density and versatility.
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