doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Pros and Cons of extending forcing cones

There is so much of this which is purely speculative, but would like a few "Explanations" of certain points. Let's examine a bit what happens inside a shotgun bbl. Upon firing the pressure rises very fast, reaching it's peak inside the chamber & then begins to fall, rapidly at first & then in a lessening curve as the shot progresses down the bbl, increasing the volume the gas has to expand in. Changing the forcing cone angle (lengthening) would give a very "Slight" increase of volume in the area, which would tend to slightly decrease pressure. A "Slight" change in friction could also accomplish the same purpose. Either would affect recoil, to the same extent & in the same direction, it affects velocity, ie increase velocity, increase recoil etc. "If" the same load is fired & achieves the same velocity, but has lowered pressure in the cone area, then it has to off-set in elsewhere. I can see no possible affect lengthening a cone can have on a thin bbl in the forward portion. If you have a bbl with good chamber wall thickness but thin forward & want to "Favor" them, shoot light loads put up with the fastest burning powder which will stay within allowable chamber pressures & forget the cones. The faster & "Less Progressive" the powder used the lower will be bbl pressure while the slower & "Most Progressive" powder used will result in higher bbl pressures. This assuming equal shot wt @ equal velocities. Chamber pressures will be the opposite. One simply needs to study the bbls in question & decide which is the most important low chamber presure or low bbl pressures. If both the only option is "Light" loads overall.

If you are going to shoot ammunition with plastic wads it is less an issue with longer cones. However, it may still be possible to get an ocassional 'blooper' due to a poor seal in cold weather or with certain less pliant synthetic wad materials.

The older abrupt or steep forcing cones pre-dated plastic wads by almost 100 years and work well with any of the card or fiber wad ammunition. If you are going to use or load card, cork or felt wadded ammunition you will be 100% better off to leave the cones alone.

I can see no reason ever for having a cone over 1.5" in length, ever. Chuck's comments mirror what the old flyer shooters figured out way back when .. a slight improvement in the pattern quality due to less pellet deformation. Remember that for the most part flyer loads at that time used card wadding and did not generally have the shot protected.

FWIW, Kreighoff's have almost no cone to begin with or about that length [1.5"]and many sporting clay type guns now sport similar long cones in their oversized bbls.

Generally speaking, your money would be many times better spent on lessons with a qualified shooting instructor. That is actually the best money one can spend on shooting, if we are to be perfectly honest about it.

775,

32", less the 3" chamber length ;-)

While I'm not of the crowd that touts long cones reduces recoil, I do believe there is more to how a person percieves recoil than the simplistic calculation using velocity, mass and gun weight. That calculation doesn't consider the nuances of time/acceleration of the mass within the barrel. Most of you here agree that the gun begins to recoil at least as soon as the load mass begins to move. I think many of you agree that different burn rates of powder will accomplish the same velocity with different peak pressure. I will go a bit further out on a limb and say many of you recognize that it takes the same total energy (a.k.a. "energy under the curve") to push a load to the same velocity no matter the time/distance to accelerate it.

So, if two loads of the very same velocity and weight of shot, using different powders, that have different peak pressures, the total energy expended has to be the same after all is done. That means the powder is exerting higher pressure further down the barrel on the lower peak pressure load. Some of us may not be able to feel that difference, some may. It's simply the inverse of how a hydrocoil "lowers" recoil. It spreads it over a longer time.

Don't make me come over there tw!

There are I know many out there with more mathamatical abilities than I. However it is my understanding a normal bbl time for a shotgun is on the order of .003 sec. Assume a 1 1/8oz charge with a combined shot & wad weight of 60 grains, fired from a 7lb gun. During that .003 second while the charge travels the length of a 218" bbl the gun will have moved (If in Free Recoil) approx 5/16" & attained it's recoil velocity. The rest of it's movement is from inertia. Personaly, I am extremely thankful that I am so totally insensitive, that from the same gun acheiving the same ballistics I can't tell if it's using Pink dot, Purple dot, & has ½" or 5½" cones.
I simply do not have the means of proving it one way or the other, but am extremely confident that such things as recoil pads, hydro-coils, gas operated autos etc which acheive lower "Felt Recoil" do so by spreading it out over a longer time frame than that .003 sec, or they are still working in the "Inertia Stage".

A longer forcing cone will reduce stress concentration at the transition from chamber diameter to bore size. From this perspective longer forcing cones are a plus.