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Understanding Shotgun Chokes

Discussion in 'Competition Shooting' started by SHOOTER13, Sep 13, 2011.

  1. Rossignol

    Rossignol The Original Sheriff Staff Member Global Moderator Moderator Sponsor

    I mentioned in another post the numbers and charts never really meant anything until I could put my hands on something tangible. Otherwise it's all rather frenetic if you will.

    Something that wasn't clear, even if its clearly mentioned here, were the differences and coorlations between constriction and exit diameter. It may be a case of not having the info side by side for comparison, but one thing for sure- while constriction should be relative, the exit diameters depending on gauge should vary.

    Here's what I mean;
    A 12 gauge has an exit diameter of .730 thousandths of an inch. If we go kinda middle of the road on constriction with .040, the exit diameter has been changed to .690 if I'm mathing properly this morning.

    This is not alternate reality stuff right?

    Ok, so I began with the 835. A 12 gauge gun. Sort of. It's a 12 gauge chamber but with 10 gauge bore dimensions which means an open cylinder exit diameter of .770 thousandths. So if we use exit diameter alone and choose a choke with an exit diameter of .690 the constriction is not .040 but .080 or a difference of 4 hundredths of an inch. It's not much but the difference moves the gun in to nearly turkey choke range or is the difference between using buckshot of any kind to switching to a goose load perhaps like BB to maybe #2 shot.

    Some very tight turkey chokes, or a choke for maybe card shooting may be a full tenth of an inch in constriction or .100. For the 835 or 935 this means an exit diameter of .670 but for the 500, 535, or 930 it would be .630.

    So while there is relativity among constrictions, (eg. modified = .020+/-), there is no relativity among exit diameters from one gauge to another.
    Last edited: Sep 7, 2015
    SHOOTER13 likes this.
  2. SHOOTER13

    SHOOTER13 Guest

    Lead shot comparison chart

    Below is a chart with diameters per pellet and weight for idealized lead spheres.


    0000------Buck--------82 grains------9.70 mm (0.380")
    000-----½Buck-------76 grains-------9.40 mm (0.370")
    000-------Buck-------70 grains--------9.14 mm (0.360")
    00½------Buck-------59 grains--------8.60 mm (0.340")
    00---------Buck------53.8 grains-------8.38 mm (0.330")
    0----------Buck------49 grains----------8.13 mm (0.320")
    #1½------Buck------44.7 grains--------7.90 mm (0.310")
    #1---------Buck------40.5 grains--------7.62 mm (0.300")
    #2½------Buck------36.6 grains--------7.4 mm (0.290")
    #2---------Buck------29.4 grains--------6.86 mm (0.270")
    #3½------Buck------26.3 grains---------6.60 mm (0.260")
    #3---------Buck------23.4 grains----------6.35 mm (0.250")
    #4---------Buck------20.7 grains-----------6.09 mm (0.240")

    FF-Waterfowl---18.2 grains-------5.84 mm (0.230")
    F-Waterfowl----16.0 grains-------5.59 mm (0.220")
    TT-Waterfowl--13.9 grains------5.33 mm (0.210")
    T-Waterfowl---12.0 grains-----5.08 mm (0.200")

    BBB-Bird------10.2 grains------4.82 mm (0.190")
    BB-Bird--------8.50 grains-------4.60 mm (0.180")
    BB-Bird-------8.10 grains--------4.57 mm (0.177")
    B-Bird--------7.40 grains------4.50 mm (0.170")

    #1---Bird----6.15 grains---------4.10 mm (0.160")
    #2---Bird----4.40 grains--------3.76 mm (0.150")
    #3---Bird----5.07 grains---------3.6 mm (0.140")
    #4--Bird-----3.30 grains--------3.28 mm (0.130")
    #4½-Bird---2.90 grains--------3.18 mm (0.125")
    #5--Bird-----2.60 grains--------3.05 mm (0.120")
    #6--Bird-----2.00 grains--------2.77 mm (0.110")
    #7--Bird-----1.50 grains--------2.50 mm (0.100")
    #7½-Bird---1.29 grains--------2.39 mm (0.095")
    #8-Bird-----1.09 grains--------2.26 mm (0.090")
    #8½-Bird--0.97 grains--------2.16 mm (0.085")
    #9-Bird-----0.75 grains--------2.01 mm (0.080")
    #10-Pest----0.51 grains--------1.80 mm (0.070")
    #11-Pest----0.32 grains--------1.50 mm (0.060")
    #12-Pest----0.19 grains--------1.30 mm (0.050")
    Dust-Pest--0.10 grains or less-1.00 mm (0.040") or less

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