1. Attention: We have put together a thread with tips and a tutorial video to help with using the new software. Please take a moment to check out the thread here: Trapshooters.com Tutorial & Help Video.
    Dismiss Notice

Help undserstanding choke constriction

Discussion in 'Shooting Related Threads' started by 8708, Aug 16, 2013.

  1. 8708

    8708 Member

    Joined:
    Jun 10, 2006
    Messages:
    94
    We all know choke constriction is the difference between bore diameter and choke diameter. What I can't get my head around is this: Barrel #1 bore = .730, choke = .700 so .030 constriction means I have a full choke. Gun# 2 bore = .740, choke = .700 so .040 constriction meajns I have an Xtra Full choke. How can I expect the pattern to differ from #1 to #2 when the exit point of the shot from the barrel (the choke) is the same? It seem to me all I would have in # 2 is a back bored barrel.

    Help me understand!
     
  2. halfmile

    halfmile Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    15,642
    Location:
    Green Bay Wisconsin
    You need a math refresher.

    .730 - .30 is .430. That's an impossibility as is your second example.

    .030" and .040" would be more the case.

    Your first example is approximately 3 percent restriction of the bore.

    4 per cent of .730 is .0292, close enough. You have reduced the bore by 4 percent.

    The second example is roughly a 5.4 per cent reduction of the bore size.

    5.4% of 740 is .03996. You have reduced the bore size 5.4 per cent.

    So in your mind, is a 5.4 percent choke REALLY the same as a 4 per cent choke?

    (there will be a quiz at the end of the class)

    HM
     
  3. dverna

    dverna Active Member

    Joined:
    Jan 29, 1998
    Messages:
    2,717
    The exit bore diameter is not the "choke". The choke is the difference between the barrel diameter and the choke diameter.

    If "choke" was primarily dictated by the diameter at the end of the barrel, a 28 ga barrel would give a tight pattern.

    Don Verna
     
    KC135NAV thanked this.
  4. Gapper

    Gapper TS Member

    Joined:
    Feb 26, 2010
    Messages:
    823
    And since the bore of the barrel is circular; not a straight distance, you'll have to do the math and consider the reduction in "area" between the two different bore sizes.


    And there are other considerations.
     
  5. BryanF

    BryanF Active Member

    Joined:
    Jan 29, 1998
    Messages:
    205
    I believe the shot also speeds up as the barrel is constricted. Mr. Bernoulli has a convincing argument in favor of this; as the volume is reduced, the shot must travel faster so as to not blow up the barrel!


    Bryan
     
  6. timb99

    timb99 Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    7,331
    Location:
    Shawnee, Kansas, USA
    Bryan F

    Our belived Mr. Bernoulli was talking about fluids, and shot is not a fluid.
     
  7. 8708

    8708 Member

    Joined:
    Jun 10, 2006
    Messages:
    94
    HM, you and I both know and understand (from the numbers) how much constriction we're talking about in the examples. I didn't ask for a math lesson, I asked for help wrapping my head around how that works. Apparently you don't know either or you would have answered the question.

    To everyone else, I appreciate the information. It makes sense to me now. The comment from Don about a 28ga barrel and how choke is not dictated simply by the diameter of the end of the barrel was one of those lightbulb moments.

    Thanks
     
  8. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

    Joined:
    Jan 29, 1998
    Messages:
    7,168
    8708,

    "How can I expect the pattern to differ from #1 to #2 when the exit point of the shot from the barrel (the choke) is the same?"

    Perhaps the shot column expands to the larger bore size as it travels towards the choke and then when it hits the choke, the larger change in constriction causes a larger difference in the final pattern. There's more for the shot column to react to, hence a tighter result.

    (Your constriction numbers are indeed off by a decimal point, but you can fix that with an edit)
     
  9. Neil Winston

    Neil Winston Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    7,848
    8708, I think you had the idea right in that first post, except for one assumption, that the 0.030 choke would be, or generally perform like, a full choke. Based on my experience, it will shoot a bit more open than a 0.040 (or even 0.035 which often, but not always, a match for 0.040.)

    In other words, your text "It seem to me all I would have in # 2 is a back bored barrel." should have added "with more choke which will shoot tighter."

    Jim Muller says that smaller (12 gauge) bores shoot tighter than larger ones. For example, Beretta 0.723 bores shoot very tightly compared to later Optima ones and the competition too. A test of mine did, in fact show that the old bores did shoot tighter than the new ones.

    In the following graph, the Briley XF chokes both had 0.040 restriction relative to the bore. I think it shows that it's not just the constriction, purely, but bore diameter may play a role too:

    BrileyXFMobilvsOpt_zps1e532b05.gif



    This is, as you likely have heard, is contrary to the party line. But I think he may be right, or at least, not wrong.

    Neil
     
  10. Neil Winston

    Neil Winston Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    7,848
    No, Mike, as many here have posted, the critical variable is "how much the shot is constricted in its travel from bore to choke" and not "what's the diameter of the shot charge when it exits."

    But as the graph above warns, there can be other controlling variables - let's call them "influences" -which in some cases may be the bore diameter itself or choke design and who knows what else.

    Neil
     
    East Texan thanked this.
  11. hmb

    hmb Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    9,429
    Shot deformity is a part of the puzzle. Some tuned barrels are designed to treat the shot gently to avoid deforming the shot. HMB
     
  12. Neil Winston

    Neil Winston Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    7,848
    HMB, though there is (at least) one inconsistent result, I've collected a lot of data showing that the theory that the choke-caused deformation is significant is not supported by experiments. Of course, it may be that I didn't do the right tests, but they look OK to me.

    For example, you have often read that "An overchoke condition results from chokes of more than 0.040 constriction and leads to blown patterns" (and so on.)

    Here's what really happens. There are no "blown patterns" whatever they are. Instead, there are just somewhat fewer tight patterns, though they are for the most part just the same as extra-full. The Carlsons had about 0.070 and 0.080 constriction and even the tightest shot only about 3% more open patterns than the very good Briley XF. And that's just a dozen pellets!

    Brileyxfisbest_zps5936bb19.gif

    Neil
     
  13. hmb

    hmb Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    9,429
    Read my post again, I did not mention choke constriction. HMB
     
  14. Neil Winston

    Neil Winston Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    7,848
    That is true, Howard.

    On the other hand, I never said your post _did_ mention choke restriction.

    Neil
     
  15. john g.

    john g. TS Supporters TS Supporters

    Joined:
    May 7, 2011
    Messages:
    433
    Most all above is correct if you do not get it by now, You need to shoot a few more years or clasify it as F.M.

    John g.
     
  16. mike campbell

    mike campbell Active Member

    Joined:
    Jun 19, 2009
    Messages:
    926
    .040" constriction has a greater choke effect in a .723 bore than a .732 bore.

    I don't see how that result is contrary to what one would expect considering what's known of choke constrictions in all of the sub-gauges, i.e., the smaller the bore the fewer points of constriction required to achieve a degree of choke.
     
  17. halfmile

    halfmile Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    15,642
    Location:
    Green Bay Wisconsin
    "How can I expect the pattern to differ from #1 to #2 when the exit point of the shot from the barrel (the choke) is the same?"

    That was your question.

    Answer: because 5.4 percent constriction is more than 4 percent.

    Certainly the patterns would differ, and that was my point.

    HM
     
  18. halfmile

    halfmile Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    15,642
    Location:
    Green Bay Wisconsin
    Mike, I believe the parallel section only has to be long enough to contain the shot charge, and more does nothing.

    (From a testing article in Shotgun Sports years ago)

    HM
     
  19. 8708

    8708 Member

    Joined:
    Jun 10, 2006
    Messages:
    94
    Thanks to all, great food for thought. As you might expect, I'm not in a position to challenge any of the theories or comments presented. I just want to understand how the whole bore vs constriction thing works. I'm getting there. Keep it coming, I'm reading and learning!
     
  20. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

    Joined:
    Jan 29, 1998
    Messages:
    7,168
    mike campbell - nice rule!

    "The smaller the bore the fewer points of constriction required to achieve a degree of choke."

    And for overbored 12 ga barrels, as described in the original question and supported by Neil's data, here is the inverse rule:

    The larger the bore, the more points of constriction required to achieve a degree of choke.

    Why? What's going on inside that barrel and choke that makes it so?
     
Search tags for this page

degrees of choke

,

ljutic choke diameter

,

too tight choke constriction results in blown pattern

,

what choke constriction is full choke