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What is the real constriction of screw in chokes?

Discussion in 'Shooting Related Threads' started by brent375hh, Nov 23, 2009.

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  1. brent375hh

    brent375hh TS Member

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    If my barrel runs .737 for its length but the entrance to all my chokes is .748, what is the actual effective constriction for a given choke?

    Lets say that a given choke measures .710 at the muzzle. Is the constriction
    .027, or .038?
     
  2. AveragEd

    AveragEd Well-Known Member

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    All choke tubes should be a little larger at their inlet than the bore diameter to keep a wad from hanging up on the tube - .005" is pretty much what most choke makers shoot for but more doesn't really hurt anything. To determine true constriction, subtract the choke's outlet diameter from the bore diameter. In your case, the constriction is .027".

    Ed
     
  3. zzt

    zzt Well-Known Member

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    Brent, there is no absolutely clear answer to your question. Technically speaking, a bore ID or .737" and a choke ID of .710" means you have an Improved modified choke of .027". Most people would say that is just the right choke for singles and short yardage handicap.

    Here is the real story. That barrel ID/choke match up is terrible. Throw themout and buy good after market chokes. Your gun, your patterns and your scores will thank you.

    Here is what is happening. It is a big no no for the bottom of the choke to be smaller than the bore. The result would be the shot hits the flange of the choke and shoots it out of the gun. To eliminate that, most manufacturers make absolutely sure the entry diameter of the removable choke is larger than the diameter of the bore. Some play it very safe, others match as close as they can.

    Let's say the manufacturer allows a +/-.002" tolerance on the bore diameter. If the nominal bore diameter is supposed to be .734", that means allowable bore diameters range between .732" and .736". Now suppose the same manufacturer allows the same tolerances for the choke tubes. Say they set the minimum entry diameter of the choke tube at .0737" to make sure that even on the largest allowable ID bore there is zero possibility the choke tube ID will be smaller than the bore ID. With +/- .002" of allowable tolerance, that means they must specify the nominal entry ID for the choke at .0739" so that the smallest possible in tolerance tube can be no smaller than .0737". That means the largest allowable tube can be as much as .0741" ID.

    If you have the smallest allowable bore of .732' and the largest allowable choke tube (entry diameter) of .0741" there is a .009" difference in diameters. That's awful. Bear in mind, +/-002" tolerance is pretty good for the gun trade.

    That means is you are not using the tapered length of the choke tube to good effect. Since the bore diameter is .732" and the entry of the choke is .0741", the "bore" actually widens as the shot passes the bottom of the choke tube. The shot expands a little, then eventually meets the choke tube and slams into it. It a very short space it must be reduced to the parallel section diameter. In your case this would be .710". In effect, you waste half or more of the valuable conical section, simply because you were unlucky in the tolerance match up. this is exactly what I experienced with the Optima chokes that came with my 682 Gold E combo.

    I replaced a lot of the chokes with Briley chokes that held much better tolerances. The result was almost the entire conical section was used, so the shot had a smoother and more orderly transition to the parallel section. Patterns improved (among other things).

    Call Wright's, Briley or Teague. Give them you barrel IDs and have them make you some decent chokes. It will not cost much, and you be much better off.
     
  4. AveragEd

    AveragEd Well-Known Member

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    With all due respect, I used to subscribe to the theory ZZT referred to - that the choke tube inlet should match the bore as closely as possible. In a perfect world, that would be great but having more than .002" of increase in the tube isn't nearly as harmful as he makes it sound. And that's according to two of the choke manufacturers he mentioned.

    It was explained to me that at the speed at which the shot, which is contained in a plastic wad that reduces its fluidity, travels past that slightly larger area of the tube, it doesn't have time to expand into that area before it contacts the tapered portion of the tube. Don't forget that the worst case scenario measurements he mentioned have to be divided in half to arrive at the actual difference at any point around the bore. Now compare even .0045" (.009" divided by 2) to the diameter of #8 shot pellets and the numbers become even less meaningful. In fact, that's less than the .005" that is sort of an industry standard.

    I've tested 10 Beretta Optima-choked barrels and every one of them threw very nice patterns. I'm a results-oriented guy and am perfectly willing to overlook what the technocrats would criticize if the results are good in spite of the numbers. In other words, if it works, it isn't broken.

    Ed
     
  5. AveragEd

    AveragEd Well-Known Member

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    The answer to your question RE: why the Briley chokes smoke or miss targets completely is simple - parallel. The Brileys I've measured have a ton of it and the more parallel a choke has, the hotter the core in proportion to the constriction. A .025" choke with a lot of parallel will hammer targets harder than a .030" tube with less parallel - if you center them. But that .030" tube will break targets into four or five pieces where that .025" will miss them.

    Now in Briley's defense, and you and I discussed this in PMs a few weeks ago, I believe Briley makes SKB's chokes to SKB's specifications. I say that because the tubes in the 85TSS I tested for Shotgun Sports Magazine had wildly varying amounts of parallel; so much so that the "modified" tube threw tighter patterns than the "full" tube because it had so much more parallel than the "full." Briley chokes seem to have more parallel than other brands but a company doesn't sell as many chokes and stay in business as long as Briley has by making chokes like those that came with that SKB.

    Get out your bore micrometer and measure those chokes. I'm willing to bet that as much as the last half-inch or more of them will have no indicator needle movement. That's parallel - the walls are parallel to each other with no taper. Chokes have to have some parallel to stabilize the shot leaving the muzzle but too much gives you unexpected results at the patterning board. In a short tube, it can also destroy the pattern through shot deformation because the tapered portion of the choke becomes so short and abrupt. Each choke is only so long and as the amount of its length that is parallel increases, the length left for taper decreases.

    Based upon how Stu Wright taught me chokes work, I would venture a guess that an extended tube would throw marginally better, more even patterns than a shorter tube with the same constriction and parallel. The difference wouldn't be tremendous but the gentler the choke is on the shot, the fewer deformed pellets in the charge and the fewer flyers in the pattern. Longer tubes of the same constriction and parallel have a less abrupt taper, thus are easier on shot than shorter ones.

    You really cannot accurately evaluate chokes and their patterns without a bore micrometer. Without one, you're flying blind and doing nothing but guessing.

    Ed
     
  6. KENENT1

    KENENT1 Active Member

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    I had a choke tube that was .004 (.002 on a side) larger than my barrel, and I missed a bird.



    tony
     
  7. Bob Hawkes

    Bob Hawkes Well-Known Member

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    The last sentence of Ed's last post says it all. The bore micrometer is the most important tool you can have if you have any interest in chokes, patterns, etc; and how they work together. It is a great educator. Shoot often while we can, Bob
     
  8. Smok'n Joe

    Smok'n Joe Active Member

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    Ed,

    I believe you are RIGHT ON with that detailed explanation. As you and I
    have discussed before, what I am trying to do is to get my SKB 85 TSS to deliver the effortless, consistent patterns and breaks that I get from my old fashion 1100 Trap fixed 30" Full. Based on what we have discussed, I am assuming that the 1100 barrel has a long gradual restriction or tapered choke that is delivering an evenly distributed shot pattern. I get very few misses and very nice centered breaks with it. More importantly, I get some "CHEAP" breaks that I can read and adjust accordingly. The bottom line is that my scores are better and my shooting experience is more enjoyable. On the other hand, the SKB gives me SMOKED targets, very good long range centered shot performance, but CLEAN MISSES and poor scores, especially from 16 yards, and it's no slouch from 27 yards either! I want the best of both...doesn't everyone? At this point, for safety and convenience, I prefer to shoot a single shot break open for Annies. I purchased the 85 TSS because it looks and feels great...now if I can get it to perform I'll be happy!

    I haven't shot the extended Carlson's chokes yet and I will let everyone know how they work out, but here's my point...now that I have a bag full of chokes
    for this "COMPETITION" grade trap gun...where do I go next if I'm still not satisfied?

    A Custome Made choke?

    A new fixed choke barrel?

    Scrap the 85TSS for an old fashion Spaghetti Gun or vintage BT-99 (ouch!)?

    How about a new 1100 or 870 Competition?

    Last option...give it up and just keep shoot'n my 1100 until it desinegrates?

    if it aint broke...don't fix it!
    Joe
     
  9. zzt

    zzt Well-Known Member

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    On Briley's web site, there used to be a section where choke tubes were discussed. It is no longer there, or at least I cannot find it. The most informative was the discussion about what their research had taught them about choke tube performance.

    One of the things that struck me was their saying research had shown that it took a 0.75" parallel section after the conical section to stabilize patterns. The entire discussion was interesting. I wish they still had it up.

    I have had several detailed discussions with ballisticians at Briley concerning choke selection. The second was when I was when I had found the chokes that came with my Beretta 682 Gold E combo deficient. Firstly, only two of the six choke tubes shot t the same POI. Secondly, the entry ID of the good ones (and the bad ones) was considerably larger than the bore diameter, and proceeded in a single taper to the parallel section. As I said earlier, the shot impacted the conical section more than halfway up. The impact generated a lot of heat and deposited melted plastic from the point of impact up to the parallel section. It was a bear to clean. If you didn't clean it, it built up, and patterns suffered. Briley uses a two tapered approach in their tubes. The very short entry taper is steep to assure there is no possibility the shot could catch the edge of the tube and shoot it out of the barrel.

    The options discussed to "fix" my 682 included rethreading to Briley's thin wall chokes, extended chokes and flush chokes. I was only interested in extended vs. flush at the time. I told them what I had found in my Optima chokes, and they were not surprised. I asked what the pattern differences would be between them. I was told that one you reached a .75" parallel length, more was not going to help. The only difference would be in the main conical section, and weight. In Optima length chokes, the differences would be minor. I opted for the flush tubes, because I didn't want additional weight at the end of my barrels.

    Patterns were better. Plastic was deposited at a 90% lower rate, and it was evenly deposited around the tube. It never built up as on the Optima tubes, and never seemed to affect patterns. BTW, ALL of the Briley's shot to the same POI.

    Some additional evidence for the benefits of "long" parallel sections are the several famous barrel smiths. None of them use a short parallel section. They all have their favorite profiles, and favorite tweaks. At least 2 out of the 3 famous smiths believe that tapers are also important, and those tapers include forcing cones. One even says that radiusing the conical /parallel transitions is a benefit. I've owned and patterned barrels from two of these smiths, and seen patterns from the other. They were all very nice.

    My Superposed barrels has long conical sections and very long parallel sections. The were the best patterning barrels I've ever owned.

    So it would see from the above, and from Ed's post, that parallel section is important, but so is the conical section. I have found that longish choke tubes generally work best, although there are exceptions.

    Wilkinson took three original, short (1.5" long approx.) flush mounted tubes and reworked them along with the barrel. The threw magnificent patterns. Go figure.

    Another fly in the ointment is Teague. He adopted the profile gunsmiths used to add choke to best shotguns after the barrels had been shortened. They swaged the barrels to provide the constriction desired. Along the way they found this produced wonderful patterns. So Teague produces choke tubes matched almost exactly to bore diameter and consist of a single conical section. There is no parallel section. The taper continues from back to muzzle end. They have a reputation for patterning tighter per constriction that "standard" tubes do. I've never patterned one, so I cannot say first hand. However, Dr. Jones, the inventor of the Shotgun Insight pattern evaluation program does, and he likes them.

    So the best I can say is, there is no simple answer. Some formulations seem to work all the time. Stu Wright uses a standard profile, as does Briley. The three barrel smith names have their own standard profiles, some more than one depending on use.

    Smok'n Joe, if you decide to buy more tubes, ask Briley whether the profiles used in the tubes they manufactured for SKB were their own, or specified. I don't know anything about any of the tubes you mentioned, so I wouldn't hazard a guess as to what results you are going to see. I will say the only SKB shotgun I owned threw patterns much as you describe, and tighter than you would expect form the Mod and Full designations. BTW, try a Mod tube in your gun for singles, or even a LM.
     
  10. BigM-Perazzi

    BigM-Perazzi Well-Known Member

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    what design did herb orre us for you old timers....or, what was the "super choke"?
     
  11. hmb

    hmb Well-Known Member

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    You can not accurately evaluate choke tubes until you shoot clay targets with them. Until then you are flying blind. HMB
     
  12. short shucker

    short shucker TS Member

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    BigM-Perazzi,

    That's what I was thinking of. I believe that I always heard it as a "Jug" choke. The area just ahead of the choke was hogged out to create a larger ID.

    I don't know about it, but a few of the ole timers swore by it.

    ss
     
  13. Chichay

    Chichay TS Supporters TS Supporters

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    Q&A about chokes in the Briley website.
     
  14. Smok'n Joe

    Smok'n Joe Active Member

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    that Q&A at Briley is a good read...thanks
     
  15. xringjim

    xringjim TS Member

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    Hey Joe, have you tried using a one-ounce load at 16. The lighter load in combination with a less constrictive tube might give you what you're looking for. Also, try loading your shells at a higher velocity. It has been my experience that hotter loads give a bigger spread. I too just bought an SKB 85ttr combo. I'm playing with it and find it quite good at breaking birds. Jim
     
  16. Andy44

    Andy44 Active Member

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    The Seminole chokes I bought for my 85TSS matched my bore size of .736 and pattern more evenly than the original SKB chokes, but have less of a "hot core". These chokes are the Competition series with a 3/8 extension. They all have identical POIs, don't clog up with any residue, and are a bargain when you can get a free one if you buy 3. Try 'em....you'll like 'em!

    AndyH ;-)
     
  17. brent375hh

    brent375hh TS Member

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    I shoot a Browning XT. My barrels measure .737 bottom & .739 top. If anybody knows of a choke that is closer to .740 at the inlet instead of .748-.750, I would appreciate the make. My IM choke runs .721, so it really is more of a modified than IM. It also has holes in the 30 yard pattern that explain some of my mystery misses on straightaways. Last week I shot the full and came up with a 96 and knew why I missed the 4. Perhaps I should just use full for singles and full and Xfull for doubles?


    While it might not make a difference, I patterned my 101 this morning, and it threw more even patterns. Could be a fluke, but the fixed chokes sure look like a smoother transistion.
     
  18. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    I measured a famous Pa. shooters Herb Orr choked Superposed years ago and the parallel section was about .004 tapered (bell mouthed)
     
  19. Andy44

    Andy44 Active Member

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    Smoke'n-Joe asked:
    " Hey Andy...what's the story on the Seminole choke tubes...I never heard of them. Website? Price?

    Tell me why you replaced the Briley internal chokes that came with the gun...I'm very interested in hearing about your experience as are quite a few other SKB shooters!!! "

    I got tired of using the choke wrench to change flush chokes! The Seminoles extend 3/8" and are color-coded for easy identification. They are probably the least expensive chokes that match my SKB barrel size of .736 without going "custom".

    A simple search will find them at www.seminolegun.com where you can find out more about them.

    AndyH ;-)
     
  20. Smok'n Joe

    Smok'n Joe Active Member

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    Andy,

    Convenience is certainly a consideration...but what I was interested in
    hearing is how do the Briley and Seminoles compare in performance? I
    purchased Carlson extended tubes for my 85TSS because I was pleased with
    the consistency I got from the Brileys chokes which seemed to produce a
    very HOT core but poor peripheral patterns. I got SMOKE on center hits
    and a lot more CLEAN MISSES than I used to.
     
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