Forcing Cones Explained


Dear Technoid,

Greetings from a beginning shotgunner. Low priority questions. I have read much of the Shotgun report and subsequently had almost decided to send my Remington 1100 Special Field in to have the forcing cones lengthened and chokes installed(It has a modified fixed choke in a 28″ barrel).

Lo and behold while linking up through SR to Timney Triggers I discovered that they remove forcing cones!! HUH? What gives here? They claim it reduces recoil and improves patterns. This is stunningly similar to the claims made about lengthening the forcing cones. A trap shooter mentioned it to me recently and I just thought he was silly and had obviously not read the Technoid! I’ve heard that Timney is reputable and I’m trying to figure this out. Please advise.

Question #2 Since I’m just getting into this (thus broke and trying to minimize the financial attention from the my spousal unit) and plan to use my shotgun for Sporting Clays are Fiocchi spreaders a good short term fix for not having interchangeable chokes? I know to truly answer this I need to go to the patterning board but I live in Chicago and that is much easier said than done. I have had two people(aforementioned trap shooter and reputable sporting clays course operator) tell me that it is a “tight modified”. Will “miking” it tell me anything? I ‘ve had a hard time getting breaks on closer targets.

Thank you for this web page and I plan to buy from amazon soon to help out.

Ed
Often confused, never scared

Dear Ed,

Allen Timney (Allen Timney, 13524 Edgefield St., Cerritos, CA 90703, tel: 562-865-0181, <www.timneytriggers.com>) is most definitely reputable and knows a lot more about the inside of a gun than I do. He actually does the work. I just blather on about it.

The problem is one of semantics. It sounds as though having forcing cones “lengthened” and “removed” are two very different things. They really aren’t. It’s really the same thing, just different words.

A forcing cone is the area of transition between the chamber of the barrel and the bore. It is also the area of transition between the bore and the choke. Both are technically forcing cones. Generally, when someone uses the word “forcing cone” they are referring to the transition from the chamber to the bore and that is how I will use the term here.

The chamber on a 12 gauge shotgun is about .800″ in diameter. This .800″ number may vary slightly, but not much at all. The nominal bore of a 12 gauge shotgun is .729″ and can vary from .720″ to .740″ or even greater, depending on the amount of backbore or overbore.

The forcing cone is the barrel taper from .800″ to .729″. It is like a tapered funnel in the barrel and provides a easy path for the shot as it goes from the cartridge to the bore. This whole thing about modifying forcing cones is all about how gradual a taper this funnel should be.

In the old days, the taper was rather abrupt, going from .800″ to .729″ in a short distance, often 1/2″ or so. This was done due to the old fiber wads. They weren’t very long and gas would leak around them if they didn’t’ get into that tight .729″ bore fairly quickly. Unfortunately, the quick taper may have been good for the fiber wad sealing, but it gave the shot a bit of a crush when it was forced though the short funnel (forcing cone). With the advent of plastic wads and their better gas seal, it was found that the taper could be more gradual to treat the shot more gently (and deform less shot).

Many gunsmiths, like Allen Timney, offer the service of converting short forcing cones to longer lengths, thus easing the shot transition and reducing pellet distortion (which produces more uniform patterns). Some people call this conversion process “lengthening” the forcing cones, some call if “removing” the forcing cones. It is really the same thing. “Lengthening is probably more common a term.

Does lengthening the forcing cone do any good? Yes, probably, but not if you go too far. Tom Roster, a Seattle gunsmith, has done a lot of work in this area and feels that lengthening the usual 1/2″ to 3/4″ forcing cone to something around 1-1/2″ to 1-3/4” is about optimal. He feels that more than that doesn’t really help. Many “competition” gunsmiths offer forcing cones lengthened to 5″ and more, so there is a difference of opinion. I don’t know if that is a “if some is good, more is better” deal, but very long cones do have a downside.

I once shot a B-25 with exceptionally long cones. The work was beautifully done, but on cold days the gun would produce bloopers with cheap, promotional loads using inferior plastic in the wad. The poor plastic wad wouldn’t seal the gasses properly in the long cones. Better quality shells worked fine.

Lengthened forcing cones are supposed to improve patterns slightly by reducing the amount of deformation of the shot. The transition from the shell into the bore is a rough jolt for the shot and a longer, smoother transition is supposed to damage less shot. Also, the smoother transition may reduce felt recoil as the shot eases into the bore, rather than jams into the bore.

Does lengthening the cones really do this? It’s all really a matter of degree and depends on what the cones are like in the first place. It definitely depends on the kind of shell you are using. Big loads react better to long cones than light ones do. I’ve had cones lengthened on a number of guns and could do a before/after study. In a couple of cases the recoil was sightly reduced and patterns improved a barely noticeable amount. In other cases, I couldn’t tell any difference. Recoil changes would be even less noticeable on a gas gun like yours. Both Tom Roster and the respected Bob Brister report bigger improvements in heavy hunting loads.

Bottom line: Extending your forcing cone out to 1-3/4″ might make a slight difference and probably wouldn’t hurt anything. I’d be careful going longer, especially in a gas gun. Frankly, if it were my gun, I’d leave it alone unless you are as sick a gun tinkerer as I am. It’s interesting to note that Japanese Brownings offer overbore barrels as an option, but they don’t offer long cones. They don’t believe in it.

As to spreaders in your Mod choke- they will help and will open your pattern by at least one degree of choke (to an IC) or perhaps two degrees with an aggressive spreader. I have had very good luck reloading with the Polywad spreader. It has opened my patterns two full degrees of choke when I use the solid disk. Victory Dispenser factory shells opened one degree of choke, but were very dirty. I haven’t tested the Fiocchi spreaders.

“Miking” (using a micrometer to measure the bore and choke of the barrel) will indeed tell you what your constriction is. The choke constriction is the difference between the bore diameter and the tightest part of the choke. You can’t tell exactly how your gun will pattern just by knowing the choke constriction because different shells pattern differently. A Modified choke throws a 60% pattern in a 30″ circle at 40 yards. That’s the definition. For the sake of simplicity, a choke with a .020″ constriction is generally considered to be Modified and should throw a 60% pattern with some shell if you look long enough. Done be at all surprised to see chokes stamped “modified” with constriction anywhere from .010″ to .025″. I think that manufacturers treat choke designations with poetic license.

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC

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