Question on body taper.

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Aldon, Dec 15, 2009.

  1. Aldon

    Aldon Well-Known Member

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    I am new to the whole wildcatting thing and am spending hours reading through old posts on this site.

    I wish to thank all the members for the time they put into this site and their pursuit of long range nirvana.

    Hopefully this question is not too ignorant.

    Is there a reason that one would avoid straightening the body taper on the 30-06? Say for instance when going to the 280AI, I would guess that you would gain some additional powder capacity by also straightening out the case wall.

    Is it due to case extraction?

    Ad if that is the case, would a sako style extractor be able to manage the process?

    Edit,

    I guess it also depends on if the case already has more than enough capacity.....I am as stated before, just getting started so my questions may be totally ignorant. I am not knowledgeable as to case capacity of the 280AI, but looking at how they beefed up the 284shehane started me thinking in this direction. Just trying to get the most out of my 30-06 action.
     
    Last edited: Dec 15, 2009
  2. RockZ

    RockZ Well-Known Member

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  3. Aldon

    Aldon Well-Known Member

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    Thanks for the link Rock.

    I was aware that the Shoulder angle on the AI was increased to ~ 40 degrees.

    At one point the article does mention straightening the case but it appears it still has the taper that the 30-06 does. It straightens the case at the top where the sharper angle increases the length a bit. Thereby increasing capacity.

    In order to clarify the question that I am trying to get answered, why would one not use a straight walled design as opposed to the slightly tapered one on the 30-06 to get a couple of more grains capacity.

    On 6mmbr site in the section on 7mm's it discusses the changes Shehane did to get the additional performance out of the 284. It says he essentially straightened the case taper an additional .010 which seems to be something one could do in addition to changing the shoulder angle when going to the Ackley AI.

    Or is this .010 straightening already part of the change when modifying to the Ackley AI?
     
  4. Aldon

    Aldon Well-Known Member

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    OK, When I compare the case drawings of between the 280 and the 280 AI on Ammoguide it does look like the case taper has been increased on the AI.

    It just does not mention how much.

    I guess that answeres my question.

    Thanks for the assist Rock.

    Aldon
     
  5. MontanaRifleman

    MontanaRifleman Well-Known Member

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    Aldon,

    Here is a link to a great site that shows case drawings and dimensions...

    page8d

    You will see that the OD of the base of the 280 Rem is .470 and the OD at the shoulder is .441. In the AI version the the wall is straightened to a .445 OD whicl leaves .025 of taper.

    I'm not a smith or chamber engineer, but I would think that a straight wall chamber in rifle cartridges would lead to stuck cases, especially with warm loads.

    Hope that helps,

    Mark
     
  6. Aldon

    Aldon Well-Known Member

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    Thanks Mark.

    That is what I was looking for.

    Thanks for the link.

    If I read throught the site over the next coupel of months I might get to where I have some limited knowledge:)

    That dimension may have been on the ammoguide drawing as well but my machinest skills are rusty to say the least.

    Aldon
     
  7. trueblue

    trueblue Well-Known Member

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    Aldon,
    You are going to need some taper in your case design, or you won't be able to eject the case after firing. I don't know at what point that happens, but I won't go much under . 020 taper, depending on the length of the case.
    Maybe a smith could chime in here.
     
  8. J E Custom

    J E Custom Well-Known Member

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    The question of taper is a good one and I will try to answer It for you.

    The more taper you have the easier it will be to extract because when the bolt is raised
    the cam action will break it free and it will extract with no drag.

    The less taper the harder the extraction because of spring back of the brass (It is
    slightly larger than the Chamber after firing) and doesn't release as quickly as a more
    tapered case.

    Most Dangerous game cartriges have quite a bit of taper for assured extraction at all
    times.

    The advantage of less tapered cases is more powder capacity in the cartridge length
    and better grip on the chamber during firing reducing bolt load.

    The minimum case taper I would recomend is .006 per inch of case (A 3" case would have
    .018 of case taper ) for dangerous game, and .008 to .010 Thousandths for the total
    length of a case that will be used for normal hunting and target shooting.

    You can go less but expect problems if the chamber is not perfect and very smooth or
    if you intend to load hot for maximum velocity.

    There are Lot's of opinions on optimum shoulder angles and I think a 37.5 degree
    shoulder is about it.most ackleys are 40 degrees and they work well .

    Blowing the shoulder out does increase powder capacity and is reported to increase
    Accuracy and be easier on the brass.

    Hope this helps

    J E CUSTOM
     
    Last edited: Dec 16, 2009
  9. Aldon

    Aldon Well-Known Member

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    Thanks JE For the detailed response.

    I doubt I will go this route but my mind is wrapped around the idea for the moment and I can not seem to let it go:)

    Would polishing the chamber and having a Sako Extractor alleviate the issues of case expansion enough.....based on educated guess, with the caveat that you have already given warning that issues could arise from doing a straight walled case.

    Is the 45-70 not straight walled?

    How do they get around the issue of case expansion on those?
     
  10. James H

    James H Well-Known Member

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    There is nothing to gain by having the walls perfectly straight only more problems.
    The 45-70 is often called a straight walled case because it is not a bottleneck case. The 45-70 tapers almost .007" per inch(each side), it is not straight walled.

    You may want to purchase Dave Kiff's Book of Chamber Prints, available at his website.

    Books - Pacific Tool and Gauge Inc.

    It will give you an idea of what works.

    James
     
  11. Aldon

    Aldon Well-Known Member

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    thanks for the book idea.

    That info in the post along with what the others have given me will put my mind at rest until I conjour up another conundrum! LOL

    Thanks everyone.
     
  12. Mikecr

    Mikecr Well-Known Member

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    +1 JE CUSTOM
    I taper .010" per inch of case body when I fill out a reamer order form.
    This has worked fine for me.

    It is possible to go totally straight, but you would be more limited in pressure potential for the cartridge. On firing, a chamber expands similar to brass, but it definitely springs back fully, or your in trouble! Not always so with brass.. And that chamber can springback to an interference fit with brass that didn't.
    With no taper, under highish pressure, the body nearest the web(thicker brass) would springback more(by relative percentage) than nearest the shoulder(thinner). So the case would be held by the chamber walls near the shoulder and drag out. Would not rechamber at all without FL resizing.
    But this would only occur with high enough pressures to cause brass yield(some loss of springback), or over annealed cases(too low on the body).
    Now high pressure to me might be common for someone else.
    But keep in mind, with enough pressure, even well tapered cases 'pop' on extraction because the brass web area can actually yield(it is technically ruined). This is often used as a pressure sign. With some cartridges, it is very accurate.
    These are now cases with loose primer pockets..

    An advantage to low taper, and high shoulder angles, is reduced case lengthening. Long cases with high taper require constant trimming, and occasional donut reaming. As mentioned, these can also affect bolt pressure.
    I don't like shoulder angles under 30.
    So far, I have never needed to trim a reload, and shoulder bumps take and hold with precision.
     
  13. Aldon

    Aldon Well-Known Member

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    Thanks for the additional knowledge Mike.

    Very educated group on this site!

    I will stick to what works well and stay away from straight taper:)