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Lengthening Forcing Cones: Downsides?

Discussion in 'Shotguns' started by ArmedBear, Apr 6, 2007.

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  1. ArmedBear

    ArmedBear Member

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    I have an old Ithaca SKB 500 20 Gauge O/U for the field and some 5-stand shooting.

    I have a friend who is an experienced gunsmith and restorer of antique guns, especially shotguns. He has my 20 for some minor stock repairs. He asked me if I want him to ream out the forcing cones while he has the gun.

    Is there any reason I shouldn't do that (assuming it's not chrome-lined, which I think not)?

    The gun has 3" chambers, and I might use 3" shells for pheasant, though I can't think of much else I'd use them for. The chokes are fixed IC/M.

    Does lengthening the forcing cones weaken the barrel for 3" or heavier 2 3/4" shells?

    Thanks to anyone who knows!
     
  2. zinj

    zinj Member

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    I have heard that lengthened cones don't handle the old cardboard or fiber wads very well. They don't expand to the bore size like a plastic wad will and thus lose velocity.
     
  3. ArmedBear

    ArmedBear Member

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    This is true. Thank you.:)

    Assuming I don't plan to shoot fiber wads, is there any other downside?
     
  4. RNB65

    RNB65 Member

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    As long as it's done by a competent smith who doesn't ream out too much steel, I don't think there's any downside to lengthening the forcing cone. Long forcing cones are pretty much standard fare on most shotguns made today. A longer forcing cone is supposed to reduce felt recoil slightly and improve patterns a bit by reducing shot deformation. Whether or not it actually does either is open to debate.
     
  5. ArmedBear

    ArmedBear Member

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    It seems that people who actually shoot the identical guns, then ream them out and try them again with the same load, under the same conditions, swear that it makes a good bit of difference in felt recoil, especially in a light gun. Patterns also improve dramatically, apparently.

    Now, I don't really buy the "overbore" crap -- bigger bores just mean lower pressure and lower velocity. And I don't want any holes drilled in my barrels, other than the one that goes down the middle.

    But I believe the guy who says that longer cones work, mainly because he's a VERY experienced old shooter, with more shotguns than I can count, who's seen and tried it all, and because he's really cynical about just about every other gun gimmick. Hell, he still shoots ancient Ithaca trap singles -- nice ones -- because he likes them best, and he breaks a lot of birds with them.

    That's not the same as a scientific test; however, a true test requires me to ream my barrels. Not really reversible.:)
     
  6. Dave McCracken

    Dave McCracken Moderator In Memoriam

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    Longer cones used with modern ammo having plastic shotcups enclosing the shot aid density, lower recoil(Though I defy anyone to notice this) and are an option that should be standard.

    Maybe I should explain the density thing.

    Pure lead is so soft it'll deform if looked at hard. Even "Magnum" shot is a bit softer than it would be in a perfect world. A long cone eases the transition from chamber to bore, keeping some pellets rounder than they would be otherwise.

    Think of a pattern you put on the board or paper. Those hits way out on the periphery are from unround pellets that were deformed at launch or made that way. They are the slowest, leave the pattern weaker and carry less energy to the target from increased drag.

    Long cones do help. They are not panaceas that will overcome the Bad Shooting Demons or poor load and choke choice.

    Just another tool to help those who have done their fit and form homework and BA/UU/R eke another target and maybe do so in more comfort.

    A couple good smiths tell me that 1.5 to 1.75" is enough. Mine run about that and they work for me...
     
  7. ArmedBear

    ArmedBear Member

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    Thank you!

    I feel better about having steel removed, now.

    With a 20 Gauge, I'd like to have all the pellets I can get, staying in the pattern.
     
  8. Fred Fuller

    Fred Fuller Moderator Emeritus

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    I'll defer to The Technoid on this one- I can say that having forcing cones done improves buckshot patterns almost universally in my experience, but said experience is very narrow by comparison.

    lpl/nc
    =====
    http://www.shotgunreport.com/TechTech/TechnicalTracts/ConesBores.html

    =======snip
    Lengthened forcing cones are the one barrel modification which
    the Technoid has found to unfailingly reduce perceived recoil and
    slightly improve pattern. John McDougall, in the Australian magazine
    Guns & Game, wrote that his tests have shown a consistent 10% pattern
    tightening when cones are lengthened. This is attributed to less shot
    deformation.

    Long cones appear to take a touch of the peak off of the recoil.
    The area under the recoil curve remains the same (Newton still has to be
    accommodated and apples still fall to the ground), but the slope of the
    curve seems to change and the recoil is drawn out a bit. This is the
    "shove vs punch" comparison which makes semi-automatics seem so soft
    shooting.

    It is vital that the lengthened cones be properly polished as any
    roughness in this area will pick up a lot of plastic from the wads. Tom
    Roster claims that the maximum beneficial cone length is 1 3/4" and that
    longer cones do not improve things. This may be so, but the Technoid
    has observed that extra long 4" to 6" cones as done by The Shotgun
    Shop and Seminole seem to be able to take an absolutely mirror polish.
    The shorter cones with their sharper angle may be more difficult to
    polish correctly and never seem to buff up as well.

    Rumor has it that fiber wads do not perform well in guns with
    long cones due to gas blowby. This is baloney. The Technoid's
    checkered past included shooting tens of thousands of 3 1/2 dram Federal
    T123 fiber wad International Skeet loads through Belgian B-25s with
    lengthened cones and there was never a problem. Modern plastic wads
    present no difficulty whatsoever and appear to be able to properly
    obturate in a sewer pipe. Long forcing cones should cost you $50 to
    $150 and are worth it.
    =======snip
     
  9. kirbythegunsmith

    kirbythegunsmith Member

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    Details

    Most Ithaca imports have chrome lining in the barrels, a typical SKB treat.

    One of the first detailed tests that I did with super-long forcing cones used an 1100 12 ga. skeet barrel and Win. AA 9's, 1-1/8 oz., with the same box of shells for the "before and after" shooting.
    Target paper about 40 x 40 (roughly) shot at 25 yards

    Before: 550 to 580 on the paper

    After: 620 to 640 on the paper, and there is only about 660 in the shell.

    Conclusion: open choke barrel that had about 10% of the total shot load that had previously been "flyers" was now hitting on the paper and the center section showed more uniformity. Where prior to cone lengthening, there were some center clusters with 2 and 3 almost touching in small groupings, afterward had more even central spread without the 2-n-3 mini-clusters.
    Center spread that is more uniform and better filled pattern fringe (by the flyers being brought into the pattern) will make you more likely to get game or targets that you intend, and less likely to wound a bird outside of the pattern zone.

    The lessened deformity of the pellets ensures straighter flight for patterns that are not tighter up close, but have less flyer spread out far. Numerous shooters have commented to me about their killing power at ranges beyond what they would have previously attempted, and this is with small gauges and fairly open chokes, to boot. Start your rounder, less deformed shot with a little more velocity, hold that velocity better, have less spread at longer ranges- now there is your recipe for improved effectiveness.

    Picture 1 is of a standard forcing cone, and some rust from owner neglect is visible, along with less than perfect chamber wall texture. A small polish would eliminate the rust, add surface smoothness without altering the dimensions, and improve extraction reliability across a wider variety of shells. The forcing cone has less shadow at 3 o'clock than other areas, and proves that the chamber/forcing cone juncture is not centrally aligned to the bore of the barrel. One side of your shot column will be hit and squeezed harder than the other side. Pattern uniformity suffers because of this seldom-recognized fact.

    Picture 2 is of a standard forcing cone lengthening, about the 1-1/2" amount typically done by most shops, and a small improvement according to tests done by Ralph Walker and others, about 30 years ago. Pronouncements from that era seem to be chiseled in stone, and inviolable, sacrosanct, and dare not be questioned in the soundness of the conclusions by any jonny-come-lately's, according to a few "keepers of the truth".
    I just wonder that since Ralph admits trying only up to the 3" length, and with his era's modern shells (aka 30 year old technology), do we leave advancements for other areas of shooting alone at 30 year old results, also?

    Picture 3 is of a super-long cone lengthening, with fine polish surface to match the interior of the Remington barrel, and picture 4 is of a slant view to show more of the surface to see that no roughness is present.

    Which do you think lets the shot flow out of the crimp easier, and which has a more gentle squeeze to gradually fit the shot stack column to the bore? Less restriction is going to create less back pressure (chamber pressure) but still have more base wad surface to apply the pressure for some length of the acceleration zone.
    That helps to explain the apparent increase in average muzzle velocity that I have chronographed testing before and after with the same shells and both barrels of a Browning B-SS 20 ga. The velocity variance between shots was sharply reduced as another benefit.

    For the real nut, I have done 12 ga. forcing cones even longer than the super-long cone pictured.

    see my previous posts for more insight from the gunsmith perspective.

    [email protected]

    The Shotgun Shop, Arnold MO 636-282-4379
    Specialty Gunsmithing, custom choke work, all gauges, thin barrels
     

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  10. foxmeadow

    foxmeadow Member

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    The only downside I know of is the hassle of getting it done. Nobody in my area does it, and being cheap, I did it myself. I rented a reamer from 4-D Products and cut the cones on my two 870s and my 1100. Before I did the work, I patterned the guns, using several brands of 00B. Average spread at 25 yds. was about 16". After cutting the cones and polishing them out,( the hard part) group size went down to 12". No noticeable recoil reduction, but most of the buckshot I tried was low recoil. I'm thinking of doing it to my longer tubes and patterning birdshot next...
     
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