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Understanding Shotgun Chokes

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

  1. SHOOTER13

    SHOOTER13 Guest

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    Shotgun chokes were designed to control pattern diameters at different yards. What is a pattern? It is just the grouping of the pellets at a given yardage. This grouping or pattern is measured by a circle diameter. This particular circle must have certain efficiency. In other words, it has to have a certain number of pellets in a given area (called distribution) for it to be labeled an efficient pattern.

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    Here is a quick reference chart:

    Shotgun Choke..... Yardage...........Shotgun Choke Restriction

    Cylinder................... < 20.......................... 0
    Skeet...........................22.5......................... .005 (of an inch)
    Improved Cylinder....... 25............................... .010
    Light Modified...............30................................... .015
    Modified....................... 32.5.................................... .020
    Improved Modified........ 35.......................................... .025
    Light Full....................... 37.5........................................... .030
    Full............................... 40+................................................. .035
    Extra Full...................... 40+.................................................... .045
    Super Full......................40+........................................................ .055

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    How does a shotgun choke actually work ?

    There are two forces that tell the story... the mechanical properties while the shot column is in the barrel and the dynamic forces of nature that affect the shot column after it exits the barrel. When the shot column meets up with the choke it forces the column to squeeze tighter together; these forces are called radial forces. Once it is out of the barrel, wind resistance and gravity act on it. When the wind comes into contact with the outside pellets of the shot column it induces spinning and they start to flare off like a ping pong ball with english on it.

    The tighter the choke the heavier the radial forces, the tighter the pellets are squeezed together so the pattern holds tighter over a longer distance.

    Conversely, the less restriction you have in the choke the more loosely the pellets are held together and the faster the pattern opens up.

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  2. Rossignol

    Rossignol The Original Sheriff Staff Member Global Moderator Moderator Sponsor

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    Excellent posting, Shooter!
    SHOOTER13 likes this.
  3. John A.

    John A. Unconstitutional laws are not laws. Staff Member Administrator Global Moderator

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    Yes, I agree that does a pretty good job of explaining that chokes squeeze the shot.

    The only thing I would add to that is the biggest thing that will affect the choke more than anything is the shot size.

    The smaller the shot (say 9 shot for instance) will be more receptive to being "choked" than larger (4 shot) for instance because of room for displacement.

    Matter of fact, I gave away a 28" mossberg interchangable choke barrel because it was choked in XX full that I wanted to use Turkey hunting and it patterned so poorly with 4 shot that I almost sold the whole gun. That is why I know this and learned it the hard way

    After I gave it to my buddy and he put it on his gun and used 7-1/2 shot with it, the pattern was better indeed. [/shoulder shrug]

    With that said, the shotgun that I have used the most, and had the best performance from is an old single shot/break down 16 ga. Stevens that my Dad gave me when I was 14. It has a modified choke and is hard to miss using 6 shot in it. It'll hold most of the pattern to about the size of a paper plate at 35 yards.

    It has killed more than everything else in my gun cabinet combined.
    SHOOTER13 likes this.
  4. SHOOTER13

    SHOOTER13 Guest

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    John A. wrote: "Yes, I agree that does a pretty good job of explaining that chokes squeeze the shot.The only thing I would add to that is the biggest thing that will affect the choke more than anything is the shot size. The smaller the shot (say 9 shot for instance) will be more receptive to being "choked" than larger (4 shot) for instance because of room for displacement."

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    My next post in this thread series...but, ya beat me to it John ! ( cough...0716 )

    Would you like to be more definitive, or should I proceed...? :twisted:

    =============================================================
  5. oli700

    oli700 12g Supporter "Philanthropist"

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    9,284
    Go on. There is more about a SG barrel that affects choke choice.
    SHOOTER13 likes this.
  6. John A.

    John A. Unconstitutional laws are not laws. Staff Member Administrator Global Moderator

    Messages:
    16,079
    [quote="SHOOTER13]
    My next post in this thread series...but, ya beat me to it John ! ( cough...0716 )

    Would you like to be more definitive, or should I proceed...? :twisted: [/quote]

    no sir, proceed right along.
    SHOOTER13 likes this.
  7. SHOOTER13

    SHOOTER13 Guest

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    Chokes may either be formed as part of the barrel at the time of manufacture, by squeezing the end of the bore down over a mandrel, or by threading the barrel and screwing in an interchangeable choke tube. The choke typically consists of a conical section that smoothly tapers from the bore diameter down to the choke diameter, followed by a cylindrical section of the choke diameter. The use of interchangeable chokes has made it easy to tune the performance of a given combination of shotgun and shotshell to achieve the desired performance.

    The choke should be tailored to the range and size of the targets. A skeet shooter, shooting at close targets might use a skeet choke (.005 inches of constriction) to produce a 30 inch diameter pattern at a distance of say 22.5 yards. A trap shooter...shooting at distant targets may use a light full choke (.030 inches of constriction) to produce a 30 inch diameter pattern at just under 40 yards.
    Special chokes for turkey hunting...which requires long range shots at the small head and neck of the bird...a hunter may use a super full choke equaling roughly .060 inches of constriction. The use of too much choke and thus a small pattern increases the difficulty of hitting the target while the use of too little choke produces large patterns with insufficient pellet density to reliably break targets or kill game.

    ( Below for Oli... ;) )

    Shotguns generally have longer barrels than modern rifles. Unlike rifles, however, the long shotgun barrel is not for ballistic purposes. Shotgun shells use small powder charges in large diameter bores, and this leads to very low muzzle pressures and very little velocity change with increasing barrel length. Since shotguns are generally used for shooting at small, fast moving targets, it is important to lead the target by firing slightly ahead of the target...so that when the shot reaches the range of the target, the target will have moved into the pattern. On uphill shooting, this means shooting above the target. Conversely...on downhill shooting, this means shooting below the target, which is somewhat counterintuitive for many beginning hunters. Of course, depending on the barrel length, the amount of lead employed will vary.

    Shotguns made for close ranges, where the angular speed of the targets is great (such as skeet or upland bird hunting) tend to have shorter barrels, around 24 to 28 inches. Shotguns for longer range shooting, where angular speeds are less (trap shooting; quail, pheasant, and waterfowl hunting) tend to have longer barrels, 28 to 34 inches. The longer barrels have more inertia, and will therefore swing more slowly but more steadily. The short, low inertia barrels swing faster, but are less steady. These lengths are for pump or semi-auto shotguns as break open guns have shorter overall lengths for the same barrel length, and so will use longer barrels. The break open design saves between 3.5 and 6 inches in overall length, but in most cases pays for this by having two barrels...which adds weight at the muzzle. Barrels for shotguns have been getting longer as modern steels and production methods make the barrels stronger and lighter as a longer, lighter barrel gives the same inertia for less overall weight.

    Shotguns for use against larger, slower targets generally have even shorter barrels. Small game shotguns, for hunting game like rabbits and squirrels, or shotguns for use with buckshot for deer, are often 22 to 24 inches in length.

    Shotguns intended for all-round hunting are a compromise...but a 28 inch barrel pump action 12 gauge shotgun with a modified choke can serve as a general all around hunting gun for small game in semi-open wooded or farmland areas where dense brush is less of a hindrance and the ability to have more reach is important. For hunting in dense brush, shorter barrel lengths are often preferred.

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    phipp13 likes this.
  8. SHOOTER13

    SHOOTER13 Guest

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    As everyone here already knows, Shotgun shells are generally measured by "gauge"... though in other locations outside the United States the term "bore" is used with the same meaning. Where as rifles and handguns are almost always measured in "caliber"...which is simply a measurement of the internal diameter of the barrel measured in fractions of an inch and consequently is approximately equal to the diameter of the projectile that is fired. By contrast, shotguns are also measured by "gauge"...which is the weight (in fractions of a pound)...of a pure lead round ball that is the same diameter as the internal diameter of the barrel.

    For example, a shotgun is called 12 gauge because a lead sphere that just fits the inside diameter of the barrel weighs 1⁄12 of a pound. This measurement comes from the time when early cannons were designated in a similar manner...a "12 pounder" would be a cannon that fired a 12 pound cannonball, thus inversely, an individual "12 gauge" shot would in fact be a 1⁄12 pounder. Thus, a 10-gauge shotgun has a larger-diameter barrel than a 12-gauge shotgun, which has a larger-diameter barrel than a 20-gauge shotgun, and so forth.

    Shotshells are loaded with different sizes of shot depending on the target. For skeet shooting, a small shot such as a # 8 or #9 would be used, because range is short and a high density pattern is desirable. Trap shooting requires longer shots, and so a larger shot, up to #7½ would be desired. The smaller the shot (#9 for example)...the more receptive it will be to being constricted or "choked" than larger shot (say #4) due to space for displacement within the load.
    ( ^^^ Thanks... John A. ;) )

    For hunting game, the range and the penetration needed to assure a clean kill must both be considered. Shot loses its velocity very quickly due to its low sectional density and ballistic coefficient. Small shot, like that used for skeet and trap, will have lost all appreciable energy by 100 yards or meters, which is why trap and skeet ranges can be located in relatively close proximity to inhabited areas with negligible risk of injury to those outside the range.

    Birdshot sizes are numbered similar to the shotgun gauges; the smaller the number, the larger the shot. For hunting, shot size must be chosen not only for the range, but also for the game. The shot must reach the target with enough energy to penetrate to a depth sufficient to kill the game. Lead shot is still the best performer for the money, but environmental restrictions on the use of lead, especially with waterfowl, require steel, bismuth, or tungsten composites. Steel, being significantly less dense than lead, requires larger shot sizes, but is a good choice when cost is a consideration. Steel, however, cannot safely be used in some older shotguns without causing damage to either the bore or to the choke of the shotgun due to the hardness of steel shot. Since tungsten is a very hard metal, it must also be used with care in older guns. Tungsten shot is often alloyed with nickel and iron, softening the base metal. That alloy is approximately 1/3 denser than lead, but far more expensive. Bismuth shot falls in between steel and tungsten shot in both density and cost.

    Larger sizes of shot, large enough that they must be carefully packed into the shell rather than simply dumped or poured in, are called "buckshot" or just "buck". Buckshot is used for hunting larger game, such as deer (hence derivation of the name), and also in riot shotguns and combat shotguns for defensive, police, and military use. Buckshot size is designated by number, with smaller numbers being larger shot; sizes larger than "0" ("ought") are designated by multiple zeros. "00" ("double ought") and "000" ("triple ought") are the most commonly used sizes.

    A standard 00 buck shell holds 7-9 pellets. Two types of 00 buckshot are commonly available...regular 00 buckshot shells, and reduced-recoil shells favored in law enforcement or home defense use. Low-recoil 00 buckshot allows the shooter to make fast follow-up shots, which may be needed in a combat situation, but are not typically required in hunting where the main goal is to cleanly take out the game with a single shot.

    For narrower patterns...a buffering material, such as granulated plastic or similar material can be mixed with the shot to fill the spaces between the individual pellets. When fired, the buffering material compresses and supports the shot, reducing the deformation the shot pellets experience under the extreme acceleration. Copper plated lead shot, steel, bismuth, and tungsten composite shot all have a hardness greater than that of plain lead shot, and will deform less as well. Reducing the deformation will result in tighter patterns, as the spherical pellets tend to fly straighter. One improvised method for achieving the same effect involves pouring molten wax into the mass of shot...which will keep it together longer, but tends to foul the barrel quicker.

    Shooting lead shot will result in more shot deformation and a wider pattern...as the lead used will have minimal alloying elements and be very soft. Spreader wads are wads that have a small plastic or paper insert in the middle of the shot cup, usually a cylinder or "X" cross-section. When the shot exits the barrel, the insert helps to push the shot out from the center, opening up the pattern...but often result in inconsistent performance. Intentionally deformed shot...ellipsoidal shape or even cubical shot will also result in a wider pattern, much wider than spherical shot, with more consistency than spreader wads. Hunting loads that use either spreaders or non-spherical shot are usually called "brush loads", and are favored for hunting in areas where dense cover keeps shot distances very short.

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  9. SHOOTER13

    SHOOTER13 Guest

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    The floor is open to thoughts, additions, diversions, detractions and other comments... :cool:

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  10. walpoler

    walpoler .410

    Messages:
    62
    Nice info!
  11. ripjack13

    ripjack13 Resident Sawdust Maker Staff Member Administrator Supporter "Philanthropist"

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    On my 835, what choke would be best with 00 buckshot low recoil shells?
    The target of my affection would be coyote.
  12. Rossignol

    Rossignol The Original Sheriff Staff Member Global Moderator Moderator Sponsor

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    Allisons 500 is a fixed full choke. She doesnt like it do to the concern of firing slugs through the full choke. I began researching constrictions and its affects on shot, much as you have done, but ran into so much contradictory info, it made my head spin... One of those issues was over slugs and choked barrels.

    If you or anyone has any definitive answers on this particularly, or even proof one way or the other, Allison and I would be very grateful!

    I'm really enjoying the thread, thank you all!!!
  13. SHOOTER13

    SHOOTER13 Guest

    As noted above...the choke should be tailored to the range and size of the target...

    A coyote tends to grow as big as a medium sized dog. Now you must decide if you want to just put it down... or drop it with minimum damage to the pelt. And at what range you are going to take it at...20, 30, 40 yards ? ...further ?

    In your case, given the load...I would go with the tightest choke I had...Full or better...keeping the 7 to 9 pellets together out to the max range for effective penetration and killing punch. Basically, you want that load to hit like a solid bullet...therefore the pellets must stay together all the way to the target.

    Having said that...

    And not knowing your State Game laws...can you use slugs ( sabot )...or even a rifle !? A shotgun would not be my first choice for yote anyway...I've always use .223...and can drop 'em if I can see 'em...range not being a problem. And damage to the pelt from a .223 is minimal...
  14. John A.

    John A. Unconstitutional laws are not laws. Staff Member Administrator Global Moderator

    Messages:
    16,079
    4 shot and coyote go hand in hand in my territory. As long as you're not trying to sell pelts.

    As for Allisons fixed full choke 500, I wouldn't try a slug through it.

    And here is what Mossberg has to say on their FAQ

  15. oli700

    oli700 12g Supporter "Philanthropist"

    Messages:
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    Rifled Foster slugs are fine through a full choke....not sure about extra full but if Allisons if straight up Full than its fine and it is the only reason "riflings" are on the slug at all
  16. ripjack13

    ripjack13 Resident Sawdust Maker Staff Member Administrator Supporter "Philanthropist"

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    Not keeping the pelt. I am going to send it's head to a friend of mine, along with the turkey heads and feet I going to get from the fall turkey season.. She makes art out of them. pretty interesting stuff too. I don't own a rifle with any significant power yet. but i do have my saiga for slugs. but i don't have a tac stock on it yet. my 835 does, so that's why i am using that. however, on my barrel it says not for use with slugs. so i went to buckshot. this is the choke i have. ( but i used my old choke for the buckshot test) i didn't want to ruin it before asking someone here. good thing you made this thread.

    12 GA TG151X (.670)

    http://www.cabelas.com/product/Truglo-S ... l+Products

    [​IMG]



    I was thinking of checking this choke out too.

    Constriction adjusts from .730 to .660 inches.

    http://www.cabelas.com/catalog/product. ... BIK-229047

    [​IMG]



    So just so I understand, my choke is .670 and the super full is .055 . So does mean that my choke is extremely tight? It was designed for competition, and i have shot it ( turkey load)...it had a nice 7" ball with a couple of strays about 24"-30" around it. I liked it. my target was a pallet...I was around 20 yards away. So i'm under the assumption that my range for it is around 20 yards. maybe a little more.


    I had put in the stock choke when i tested the buckshot. on the choke tube it says...
    "ulti full turkey choke lead shot only" .....and on the other side it says

    "mossberg
    ACC or AOO" I'm not sure which letters.....its really faded.
    but its from mossberg.

    I just wanted to try it out to see if my safety clicked back on, like NASA's 835 did. he had to put an additional stretch in the detent ball spring. Mine was fine. All good. However i didn't pattern it. Just shot it into a mound of manure in the field...

    ok. I'm done pickin your brain for now, I need to hit the hay. early day tomorrow.

    thanx shooter.
  17. Rossignol

    Rossignol The Original Sheriff Staff Member Global Moderator Moderator Sponsor

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    Thanks Oli, and John!

    This is where the conflicting info comes in. Allisons barrel is a fixed full choke, and as you mentioned Oli, the riffled slug should be fine, thats what the rifling is for. And John, just as you posted, thats the sort of "official" info I run into. I have heard of people using the rifled slugs through a full choke, but I have yet to hear anyone say he or she has done it and no issues... or I blew off half my support hand, dont do it.
  18. SHOOTER13

    SHOOTER13 Guest

    Well ripjack...if that's all ya got...use all ya got. If you're not worried about the pelt...then have at it with the load you chose and the chokes you have...you'll be fine. Just aim for the body if you want the head.

    BTW...Your choke is measured in micrometers...my 1st list (above) is showing fractions of an inch.

    Meaning your .670 choke is an Improved Modified...remembering that it screws into your barrel and then further constricts down to .635 = .025 = IM

    And at the yardage you describe testing on the pallet ( 20 yds )...damn right it's gonna be a tight group...( but good luck getting a yote in that close !! )

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    Here's a list that breaks that down:


    Micrometers..................Inches..................American Name

    0.................................... .000......................... Cylinder
    127................................ .005......................... Skeet
    254................................ .010......................... Improved Cylinder
    381..................................015......................... Light Modified
    508................................ .020......................... Modified
    635................................ .025......................... Improved Modified
    762................................ .030......................... Light Full
    889................................ .035..........................Full
    1143.............................. .045......................... Extra Full
    1270.............................. .055......................... Super Full

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    Hope I made that clear... :cool:
  19. oli700

    oli700 12g Supporter "Philanthropist"

    Messages:
    9,284
    I have shot a Foster slug through a full choke.....multiple times
    Don’t know how it will affect a 20 gauge but in a 12 it makes a 2 3/4 feel like a 3” mag
    Don’t know about sabot’s never shot one, never even talked to anyone in person who has but I did sleep at a Holiday Inn last night
    ripjack13 likes this.
  20. Rossignol

    Rossignol The Original Sheriff Staff Member Global Moderator Moderator Sponsor

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    Hmmm, this would be a .410 and the constriction is very close.

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