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Thread: Question for the gunsmiths

  1. #1

    Question for the gunsmiths

    Say a rifle manufacturer has a new rifle model out.
    they come with a choice of wood or vinyl stocks
    stainless or blued barrel
    varmint or sporter profile

    that is two stocks each in two profiles and two barrels also each with two profiles that need to be manufactured
    a variety of twists to suit but a lot are 1:10"
    then they offer chambering from .243, .260, 6.5x55, .270, .308, .30-06, 300WM etc etc
    so you have two action lengths and a variety of bolt face sizes to match cartridge.


    I am making the assumption that the only difference between the barrels is once they have been chambered.
    They take a .30 calibre sporter barrel and and chamber it in .308 or .30-06 or 300WM

    Now my question (after a long ramble!) is:

    What makes a barrel with a fixed external profile a 62,000 psi, a 60,200 psi or a 64,000psi rated barrel just because the chamber is different?


  2. #2
    Quote Originally Posted by bewsher500 View Post
    Say a rifle manufacturer has a new rifle model out.
    they come with a choice of wood or vinyl stocks
    stainless or blued barrel
    varmint or sporter profile

    that is two stocks each in two profiles and two barrels also each with two profiles that need to be manufactured
    a variety of twists to suit but a lot are 1:10"
    then they offer chambering from .243, .260, 6.5x55, .270, .308, .30-06, 300WM etc etc
    so you have two action lengths and a variety of bolt face sizes to match cartridge.


    I am making the assumption that the only difference between the barrels is once they have been chambered.
    They take a .30 calibre sporter barrel and and chamber it in .308 or .30-06 or 300WM

    Now my question (after a long ramble!) is:

    What makes a barrel with a fixed external profile a 62,000 psi, a 60,200 psi or a 64,000psi rated barrel just because the chamber is different?

    I'm no gunsmith and I may have misunderstood the question, but surely the limiting factor in any chambering is the cartridge design itself rather than the barrel, hence the use of a small rifle primer in the 308 Palma allowing it to operate at higher pressures in an ordinary 308 chambered rifle.
    Im guessing that your wanting to rechamber an existing rifle to a more powerfull caliber?
    dcg

  3. #3
    Quote Originally Posted by bewsher500 View Post
    What makes a barrel with a fixed external profile a 62,000 psi, a 60,200 psi or a 64,000psi rated barrel just because the chamber is different?

    The proof marks.

    Neil.

  4. #4
    all barrels would have a large safety factor built in and as long as they pass proof then it makes little difference 4000 psi either way.

  5. #5
    Barrels must be able to take more pressure than the cartridge rating.
    The pressure rating of a cartridge leads to its design in case wall thickness. The case must seal reliably within a pressure range.
    The case must flex and stretch to seal, too much pressure leads to too much flex and possible rupture, too little pressure leads to blow back
    because the case doesn't expand enough to seal in the chamber.
    edi

  6. #6
    As I thought
    So any concerns about rechambering a 30-06 to 300WM on pressure grounds are likely to be unfounded as the case is the limiting factor not the barrel wall?

  7. #7
    Quote Originally Posted by bewsher500 View Post
    As I thought
    So any concerns about rechambering a 30-06 to 300WM on pressure grounds are likely to be unfounded as the case is the limiting factor not the barrel wall?
    well the 300wm is a fatter cartridge so you would be reducing the chamber wall thickness so yes you would be reducing it's strength but wether it's enough to be a problem , i don't know?

  8. #8
    These days not so much.

    All modern barrels tend to be made of the same spec material, so if someone is producing a 30cal barrel, it may be made of 4140 and the test pressure of the actual cartridge is largely irrelevant, other than for testing/proof.

    However as little as 20-30 years ago this was not the case, since the modern principles of steel grades and traceability were seen as very expensive, so gun makers tended to pick steel very much on its individual quality, so they would test batches of the steel, and the better ones were reserved for the higher pressure cartridge types.

    So in a 20+ year old gun, the quality of steel was chosen based on the type of cartridge being chambered.

    Plus of course the repeated firings since then would work-harden the steel

    So if re-chambering up a grade, either use a better or newer version so for example it's best not to select an old Mauser action, but perhaps a VZ24 - even then it could fail proof.

    Julie

  9. #9
    Quote Originally Posted by Julie View Post
    These days not so much.

    All modern barrels tend to be made of the same spec material, so if someone is producing a 30cal barrel, it may be made of 4140 and the test pressure of the actual cartridge is largely irrelevant, other than for testing/proof.

    However as little as 20-30 years ago this was not the case, since the modern principles of steel grades and traceability were seen as very expensive, so gun makers tended to pick steel very much on its individual quality, so they would test batches of the steel, and the better ones were reserved for the higher pressure cartridge types.

    So in a 20+ year old gun, the quality of steel was chosen based on the type of cartridge being chambered.

    Plus of course the repeated firings since then would work-harden the steel

    So if re-chambering up a grade, either use a better or newer version so for example it's best not to select an old Mauser action, but perhaps a VZ24 - even then it could fail proof.

    Julie
    Other than in the case of rimfires and black powder, I don't think that's true. (At least in that time frame) It makes no sense financially to have multiple grades of steel for a barrel making operation based on the chambering. When Remington makes a .224" barrel blank they won't bother as to whether it becomes a .222 or a 22-250.

    As to pressures, it's not the barrel, it's the breech.~Muir

  10. #10
    Quote Originally Posted by Muir View Post
    Other than in the case of rimfires and black powder, I don't think that's true. (At least in that time frame) It makes no sense financially to have multiple grades of steel for a barrel making operation based on the chambering. When Remington makes a .224" barrel blank they won't bother as to whether it becomes a .222 or a 22-250.

    As to pressures, it's not the barrel, it's the breech.~Muir
    Definitely - as late as the mid 80's some of the former eastern block countries were still using the batch test process because of un-reliable steel production, not so in the UK and most of Europe as these had already standardised - notably the EN series etc.

    Agree it is not just the barrel, it is the whole lock (not stock) and Barrel - the action and bolt are equally important, and the selection of steel wasn't just for the barrel.

    Personally for actions, and bolts I have always used 4140/4130 - barrels tend to be dictated by the manufacturer but are also now 4140 or similar (unless stainless)

    Anyone who has threaded old barrels will notice the differant quality of steel used between makes and ages and sometimes calibre

    Julie

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