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Backboring And Shot Wad

Discussion in 'Shooting Related Threads' started by pendennis, Jan 31, 2008.

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  1. pendennis

    pendennis Well-Known Member

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    All, I finally got my 90T barrels miked, and they are as follows:

    Barrel 1 - Bore=.752", fixed choke, tapers to .724 - Constriction .028, ported.
    Barrel 2 - Bore=.744", Colonial (.795 "True Tube") choke tubes, (IMP-.720, MOD-.710, IM-.704)

    The question arises now about the action of the wad, approx. .701" diameter. Does a certain amount of gas bypass the wad, or does the force of the charge cause the wad to fill the bore? If this isn't so, doesn't the shot velocity drop because of the bypass, and not getting the full amount of gas behind the wad and shot? Besides the gun weighing 10 lbs., it's very soft recoiling.

    Second, in barrel 2, even though the choke tubes have their own designation (i.e. IMP, MOD, IM), don't you end up with effectively full, and extra full, based on the actual constriction (i.e. IM@ .704=.40 constriction), thus is extra full in reality?

    I'm not trying to overly complicate this, but am I looking at things too literally, or do I have only measurements for comparative purposes?

    I'm going to do some serious patterning sessions to seek optimized usage, but I'd like to get your various takes on this.

    Thanks in advance.

    Best,
    Dennis
     
  2. ec90t

    ec90t Guest

    Dennis,

    Don't worry about wad seating unless yopu use a very light PSI load.

    As far as your barrels, The only one you'll ever need is the .028 restriction. It will absolutly desintigrate a target from distance without any peroblems unless someone has messed it up!

    ec90t
     
  3. Shooting Coach

    Shooting Coach Well-Known Member

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    As long as you keep pressures at or above 9000 PSI you will have only good results with your barrels.
     
  4. hmb

    hmb Well-Known Member

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    If it doesn't seal in the back it will seal in the front. HMB
     
  5. phirel

    phirel TS Member

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    Dennis- You have poised an interesting question about gas blow-by and reduced chamber pressure. Unfortunately, the answer to your question is not simple. First, the answer cannot be reached by checking velocity. It can only be answered by measuring chamber pressure. Chamber pressure and shot velocity are not always directly related. Also, the answer could be different for a wad with a long over powder cup than a wad with a shorter over powder cup.

    The only way I know how to get a good answer to your question is to have several barrels made for a pressure gun. You could then shoot one brand of wad through one barrel. Then, open the barrel and repeat the test. The cost/benefit of such an experiment would not be favorable.

    HM- Can you explain how the front of the wad can seal 9,000 PSI pressure behind it?

    Pat Ireland
     
  6. hmb

    hmb Well-Known Member

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    Pat,

    The lead shot pressing against the wad petals forms a seal at the front. Hard to believe, but true. I will give you an example which proves this bizarre concept. The small sub gauge tubes that you place in a 12 guage barrel, the ones that are only slightly longer than the 20 guage shell you are going to shoot in the 12 guage bore. The cup at the base of the 20 guage wad is too small to seal in the 12 guage barrel (the ulimate backbore). But never the less a seal is made, at the front. If this weren't the case I would not be able to smoke targets using 20 guage shells in my k-80 34" top single. HMB
     
  7. philip austin

    philip austin TS Member

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  8. gun1357

    gun1357 Active Member

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    A stack of round balls acts more like a liquid than a solid and will follow rules of fluid dynamics. If you have 9,000 psi pushing up from the bottom, you will have almost the same pressure pushing out toward the sides at the bottom of the shot column. If you look at a used wad you will see the shot has deformed the wad fingers/petals near the bottom about the same as the bottom surface. Other examples you may have experienced in your life might be when the lower part of a grain bin let loose in the barn, when the lower end of a concrete form gave way, etc.

    I had enough problems with the .800 bore sealing that I have gone down to .784 and had more consistent results. Your mileage may vary. Ron Renouf
     
  9. hmb

    hmb Well-Known Member

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    Alot you know, marksmanship is genetic, passed down from father to son, and it don't perish. HMB
     
  10. Neil Winston

    Neil Winston Well-Known Member

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    ... or even, sometimes, father to daughter, right hmb?

    Neil
     
  11. hmb

    hmb Well-Known Member

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    Neil,

    A very astute observation on your part. HMB
     
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