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 Post subject: Measuring choke restriction....?
PostPosted: Thu Oct 20, 2011 6:03 pm 
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On extended choke tubes, how far down from the muzzle end should the ID measurement be taken to determine the actual restriction in .000". I know that the amount of restriction is related to the actual bore size, but in this case the bore size is the standard American 12ga .729 dia. I have checked a few of my factory furnished choke tubes, and the actual restrictions DO NOT match up to the markings, IC, MOD, IMP MOD, etc. ??
Thanks, :? :?:




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 Post subject: Re: Measuring choke restriction....?
PostPosted: Thu Oct 20, 2011 6:15 pm 
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To determine the amount of constriction you MUST measure the bore (not just guess it as standard .729") then you must measure the choke tube in question at its smallest inside diameter......do the magic of mathematical subtraction and vi-ola you have the amount of constriction or if you prefer...restriction.....this may or may not coincide with the accepted but largely meaningless terms of Full, Improved Modified, Modified, Improved Cylinder, or the even more meaningless and obscure light full, lite mod or lite I/C........you must then shoot it/them at paper......
As to your original manufacturer supplied chokes; They make their chokes to their own specifications.....strangely an original manufacturer often thinks they know something about the patterning needs of their own guns....strange huh?.....go figure......Art

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 Post subject: Re: Measuring choke restriction....?
PostPosted: Sun Oct 23, 2011 10:42 am 
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How are you measuring your chokes? If you don't have a bore gauge, you may be spinning your wheels. Some chokes have a continuous taper. What this means is they must be measured at the very end to know the final constriction. Some chokes have a parallel portion. Some chokes have weird shapes. Consider these pictures:
This is what a normal choke looks like:(the drawing is exaggerated so you can see the design)
Image

This is what my Ljutic chokes look like:
Image

Every manufacturer is different. So, we can't tell you a specific depth to look for.

In the end, the actual diameter of the choke doesn't matter. What matters is how large a pattern do they create at 40 yards? That is the definition of a choke, not the tube diameter.

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 Post subject: Re: Measuring choke restriction....?
PostPosted: Sun Oct 23, 2011 11:04 am 
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Rastoff wrote:
How are you measuring your chokes? If you don't have a bore gauge, you may be spinning your wheels. Some chokes have a continuous taper. What this means is they must be measured at the very end to know the final constriction. Some chokes have a parallel portion. Some chokes have weird shapes. Consider these pictures:
This is what a normal choke looks like:(the drawing is exaggerated so you can see the design)
Image

This is what my Ljutic chokes look like:
Image


Every manufacturer is different. So, we can't tell you a specific depth to look for.

In the end, the actual diameter of the choke doesn't matter. What matters is how large a pattern do they create at 40 yards? That is the definition of a choke, not the tube diameter.


"Rastoff"... Great information/sketches. That is why I asked. Measuring is difficult if it is a continuous taper, though I believe most chokes do end parallel. You can obtain decent measurements with a quality telescoping gage and good 1" micrometer, even at the end of a tapered style. Good info... thanks, :)


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 Post subject: Re: Measuring choke restriction....?
PostPosted: Sun Oct 23, 2011 11:22 am 
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I don't think that screw in chokes are measured against the bore diameter. The entrance diameter of a screw in is usually a couple of thousandths larger than the actual bore diameter. This is so the wad and shot will not get hung up on the transition. As such, screw ins tend to act like a jug or Tula choke. Measure the entrance diameter and the smallest diameter to get the constriction.

Frank

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 Post subject: Re: Measuring choke restriction....?
PostPosted: Sun Oct 23, 2011 12:52 pm 
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Frank Lopez wrote:
I don't think that screw in chokes are measured against the bore diameter. The entrance diameter of a screw in is usually a couple of thousandths larger than the actual bore diameter. This is so the wad and shot will not get hung up on the transition. As such, screw ins tend to act like a jug or Tula choke. Measure the entrance diameter and the smallest diameter to get the constriction.

Frank


Frank; That ain't right...of course the entrance to the rear of the choke needs to be bigger than bore so there isn't a danger of catching the wad....but the distance that the greater dia of the screw in choke "lead" is very short...certainly much too short as to act or function as a jug............to the original poster....with a snap gauge and mic. you can get a good idea of the amount of constriction/restriction of your choke by comparing the difference between the bore (as measured) and the smallest dia of the choke tube....the greater dia at the beginning of the choke tube (the lead) does not act or function as a jug space nor a similarly functioning "Tula Choke"....honest........Art

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 Post subject: Re: Measuring choke restriction....?
PostPosted: Sun Oct 23, 2011 1:14 pm 
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ID of your barrel minus exit diameter of your choke tube.

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 Post subject: Re: Measuring choke restriction....?
PostPosted: Sun Oct 23, 2011 2:02 pm 
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RandyWakeman wrote:
ID of your barrel minus exit diameter of your choke tube.


Yes, but look at the variations of comments. With the variations in "true" bore diameters, the manufacturers markings, i.e., C, IC, Mod., etc. almost become useless. Pattern tests are the final word. :?


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 Post subject: Re: Measuring choke restriction....?
PostPosted: Mon Oct 24, 2011 8:20 am 
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That wasn't your question though. It is constriction and that's how it is measured. The shell has a lot to do with pattern %.



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