Ackley Headspace Gauges

Discussion in 'Gunsmithing' started by BRIT, Aug 30, 2010.

  1. BRIT

    BRIT Well-Known Member

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    Hi Gents

    My Smith has 30-06 Ackley go and no go gauges from PTG. He intends to build me a 25-06 Ackley and has said he can use the 30-06 Ackley gauges to do this as the two cartrdges share identical headspace dimensions.

    Is this correct as i note that PTG list seperate part numbers for the 2 cartridges?

    Thank you.

    BRIT.
     
  2. J E Custom

    J E Custom Well-Known Member

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    I don't think they are the same but I dont have the chamber specs.
    for a 25/06 AI to compare it with.

    Most of the Ackleys have different COL . so I would recomend that you call Dave Manson
    at 810-953-0732 and ask him (Manson Precision Reamers) or Dave Kiff at PT&G.

    Your smith may be right but if he is wrong he will be grateful for the information .
    Better safe than sorry.

    J E CUSTOM
     

  3. NesikaChad

    NesikaChad Well-Known Member

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    I have the reamer print book published by David Kiff/PTG.


    30-06 AI length from case head to datum line on the shoulder: 2.0773"

    25-06 AI length from case head to datum line on the shoulder: 2.1127"


    For reference, the datum line of the shoulder is where it measures 3/8" of an inch in diameter.

    Based on the print, if your gunsmith were to use the 25-06 gauges the cartridge would not technically be an AI 30-06 as it'll end up longer.

    In practice it's going to resemble something like a Gibbs/Ackley inbread deliverance thing that goes bang. You can't just pull material out of thin air and in this situation it's likely the case will steal material from the neck area in order to fill the dimension.

    NOW, that being said, you could probably still use the gauges. You have a couple options:

    1. If your guy is "Johnny on the spot" he can chamber the gun and headspace the gun to have the GO gauge stick out the ass of the chamber by the difference.

    OR (and if your really a wildman)

    Just chamber the thing to the 25-06 depth and run it. All your going to do is have a neck a smidge shorter than the next guy's. If you have good dies it will very likely not hurt a thing.


    IF you do this just be sure to do the following to avoid going to the hospital:

    On your initial fire form use a heavy bullet, a moderate charge and SEAT THE BULLET LONG< LONG< LONG !!!!

    LONG I SAY!!

    Here's why. With a gun being nothing more than a pressure vessel and brass being nothing more than a balloon you have pressure exerting at a right angle to whatever it contacts. That being said you want to ensure YOU are controlling where the brass stretches. By seating your bullets long you ensure your case is firmly planted against the bolt face. This offers only one choice to the case; it has to pull material from the neck and grow only towards the muzzle end of the chamber. This is harmless as the backside of the case maintains integrity. All widgit wildcats fire form like this.


    It's when you have a case rattling around in a chamber like the proverbial sausage fest/hot dog hallway analogy that you run into problems/broken parts (to include body parts)

    If the pressure exerts at a right angle the bulk of the case surface area is against the inner walls of the chamber. The brass will literally "bite" and hold fast (especially in an AI since there's almost no case taper) If the brass has nothing in front of it to ensure your case head is supported then guess what? When the primer gets whacked everything tries to move forward until either the bullet or case shoulder stops it. Then the fire gets lit and the case head stretches right back to the bolt face. Again that material has to come from someplace. In this case its from the case body, making for thin webs that love to split due to work hardening and/or pressure. If this only happened one time, its likely you'd be fine. Where it becomes a big issue is when you go and size your brass to run like a raped ape (short shoulders etc) Now your stretching it over and over and over, pulling from web/body everytime and then squishing it back into shape.

    Brass will only tolerate this for so long. Your gun will "sneeze" and you'll be picking crap n brass from your face.

    Point is you now have a case that wants to kill you when you least want it to. . .

    In your situation all a guy has to do is ensure the bullet is long and then fire form. Once you do this adjust your dies to size the case just enough to facilitate good feeding/extraction.

    Best advise, get the right gauges. PTG (David Kiff) sells em for under $30 bucks. Can't go wrong with proper instrumentation/gauging.

    Hope this helped.


    Chad
     
  4. J E Custom

    J E Custom Well-Known Member

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    +++++1

    That's good to know Chad !

    I didnt think it was the same but didn't know for sure, and I never assume anything when it
    comes to chambers and headspace.

    It worries me that a gunsmith would assume something like that, Oh Well, it's a good thing
    you questioned the use of the different headspace gauge.

    As the owner of a custom rifle everyone should be fulley aware of the chamber dimensions
    and the head space that the smith intends to give you and why.

    Some times a smith will use a reamer that will work but may not be exactly what you want
    just because he has one. and doesen't want to charge you for one. (Not a good reason)
    Get what you want even if you have to buy the reamer your self.

    I have rechambered many rifles with a chamber that would not work unless the shooter/owner
    loaded special brass, seating debths and even bullets with odd diamenters.(One had a barrel
    with a bore dia. of .3085).

    It is allways good to ask questions to be sure.

    J E CUSTOM
     
  5. BRIT

    BRIT Well-Known Member

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    Gents
    Wow. Thank you very much for the very detailed answers and for taking the time to help me out. Must have taken some typing time for which i am very gratefull.

    Just a couple more questions if it`s not rude to take more of your time please.

    If,as i said, the 30-06AI gauge at 2.0773" is used to headspace a 25-06AI that should be 2.1127" then the chamber will on the tight side? Would the resulting 2.0773" chamber accept a factory 25-06 rem cartridge for fireforming? I am not sure of the headspace dimensions of SAAMI produced ammo.
    Also why do the two Ackleys mentioned have different headspace dimensions when they both share essentially the same parent cartridge? I have looked at some case drawings for both 25-06 and 30-06 and it would seem that the only difference is the neck diameter, all other dimensions being identical.
    I hope these questions make sense.
    Thanks again for your time.

    BRIT.
     
  6. fj40mojo

    fj40mojo Well-Known Member

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    I believe the reason for the changes is to prevent chambering of similar cartridges in the wrong gun that would result in catastrophic kabooms.
     
  7. BobbyL

    BobbyL Well-Known Member

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    Most of the time the AI headspace gauges are not any different then the parent case so they from without have to do what chad said and seat the bullet long. But like he said it doesnt matter what you space it to if you are forming the brass to your chamber correctly and your FL die will bump the shoulders. The other way is to create a false shoulder by necking them down from a large caliber with a neck of fl die and start it high. Push the new shoulder back until the case barely chambers and then you have something to hold the case head up against the bolt head. It all depends on who made the reamers and how they setup the chamber.

    bobby
     
  8. BobbyL

    BobbyL Well-Known Member

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    Yes that is the smarter thing to do.
     
  9. NesikaChad

    NesikaChad Well-Known Member

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    As for why the different lengths.

    Different lengths certainly do help prevent the act of trying to insert cartridge "A" into gun "B".

    There may be another reason though.

    As we discussed earlier, the case body takes material from the neck to inflate the case and alter the shoulder angle. How much neck gets left over becomes a function of the case body diameter and length before the shoulder. Shoulder angle also plays into this. An aggressive shoulder angle is going to be shorter in length than a shallow one.

    I think PO Ackley may have wanted to have his neck lengths more uniform/symetrical from one cartridge to the next. Meaning a 25-06 should look proportionally similar to a 30-06. This would be so that bullets have sufficient support along their bearing surface by the neck. That being said the case cartridge length would have to be altered to achieve this due to the larger bullet diameter. (more circumference eats more material, ='s a shorter case length)

    I don't know this for sure, but it seems to make sense.

    If not, you'd end up with the "Ackley/Gibbs inbread thing" I described earlier.

    C
     
    Last edited: Aug 31, 2010
  10. fj40mojo

    fj40mojo Well-Known Member

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    Off topic sort of but along the same lines: i understand the mechanics of seating bullets out to the lands to hold the head firmly against the bolt face to properly fireform the case, but why have I heard that one of the benefits of the Ackley cartridges is the ability to fire factory ammo when in a pinch and end up with a fire formed case? Is this a fallacy or are all the Ackley reamers designed with the ideal throat to have factory ammo touch the lands? I don't see how that could possibly be considering all the bullet designs that were in use with factory ammo when Ackley was designing his cartridges let alone now.
     
  11. BobbyL

    BobbyL Well-Known Member

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    Thats what i was talking about. If you headspace the AI chamber with the parent cases headspace gauge you will be able to fireform with factory ammo and not have to worry about the forming. Fire forming can be your most accurate rounds out of your gun.