Do longer forcing cones lower felt recoil?
Yes, theoretically, but only to a point. The shotgun ballistics experts I consult with agree that most of the recoil from a shotgun occurs in the first four tofive inches forward of the chamber, as the shot and wad are expelled from the shell casing and reach the bore. As the wad and shot exit the shell casing, they encounter a short, tapered section of the barrel between the chamber and the bore. This is known as the forcing cone, because the shot and wad cup are forced from the larger diameter chamber (about 800/1000ths of an inch for 12 gauge) to the narrower diameter barrel (about 730/1000th of an inch). This increases friction as the wad makes contact with the wall of the tapered forcing cone and makes its way into the bore.
Imagine that you have two barrels with identical chamber and bore diameters, but one has an abrupt taper between chamber and bore, say two inches in length, and the other has a more gradual four-to five-inch taper. If using the same shell, shot and load in both barrels, you can imagine that the barrel with the longer and more gradual taper (lengthened forcing cones) would result in a less abrupt entry of the wad and shot into the barrel. While there is some disagreement among experts as to how long is long enough for forcing cones to reduce felt recoil, the general consensus is that four to five inches is optimal. Beyond that, there is nominal additional benefit.
Now for the “but.” The optimal length of forcing cones for a given shotgun is highly dependent on the shell you are using. The variables of shell speed, wad and shot composition (lead vs. steel) as well as shell and chamber length can all affect the calculation of the optimal bore and forcing cone dimensions for a given shotgun. Additionally, some UK-based shotgun manufacturers have reported that shotguns with lengthened forcing cones perform poorly when shooting shells with fiber wads.
Don Currie is NSCA’s Chief Instructor, an Orvis Wingshooting School instructor, and Master Class competitor. To get free shooting tips and videos, sign up for his monthly newsletter. You can also see more tips from Currie at www.doncurrie.com.