338 ultra mag to 300 ultra mag.

Discussion in 'Reloading' started by 6x6 elk, Apr 6, 2015.


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  1. 6x6 elk

    6x6 elk Well-Known Member

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    This may be a dumb question, but can 338 ultra mag brass be resized to 300 ultra mag? And if you can, is it just a matter of running it through a 300 ultra mag resizing die? Thanks.
     
  2. Rich Coyle

    Rich Coyle Well-Known Member

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    The .300 brass is .090" longer than the .338.
     
  3. J E Custom

    J E Custom Well-Known Member

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    The 338 RUM is .080 to .090 thousandths shorter than the 300 RUM so you would end up with a neck length 0f .215 if
    you fire formed 338 RUM in a 300 RUM chamber. Some would consider this to short.

    There are some fine 30/338 RUMs if you wanted to change barrels and use your 338 RUM brass.

    J E CUSTOM
     
  4. 6x6 elk

    6x6 elk Well-Known Member

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    The reason I am asking this question is that I have a 300 ultra mag, and like everyone else, I am having a hard time finding brass. But I know where I can find 100 pieces of 338 ultra mag brass.
     
  5. J E Custom

    J E Custom Well-Known Member

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    My brother-in-law has the same problem and has been buying the Remington managed recoil ammo
    for $35.00 to $38.00 a box when he can find it.

    It is the same brass and he uses it for range ammo and then loads it up for hunting.

    J E CUSTOM
     
  6. 6x6 elk

    6x6 elk Well-Known Member

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    I was at a gun show and someone had nosler custom 300 rum in 165 gr partition for $40. I bought the 2 boxes he had for the brass
     
  7. jfseaman

    jfseaman Well-Known Member

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    That's a great deal!.

    I bought some Reminton Premium copper for the same reason. I tried them in my rifle and darned if they don't shoot lights out so they are getting saved for hunting.
     
  8. jfseaman

    jfseaman Well-Known Member

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  9. 4xforfun

    4xforfun Well-Known Member

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    Since the shoulder on the 338 is shorter than the 300, all you need to do is treat it like the false shoulder dasher guys do when they form their Dasher brass from 6br. When you neck the brass down, leave a false shoulder to head space on. I also like to jam the bullet.

    I am not sure how much the short neck will affect things. i would watch for a carbon ring in the throat area.

    The pic is a prepped 6 BR and ready to FF to dasher.
     

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  10. Rich Coyle

    Rich Coyle Well-Known Member

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    I purchased some .300 RUM brass here and will push the shoulder back about .090" to match the .338 RUM and neck them down to 6.5mm. I plan to fire some next week!
     
  11. jfseaman

    jfseaman Well-Known Member

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    The usual 300 RUM neck length is ~.306

    Forming as you suggest would result in a neck length of .216 or less.

    While there are designs with this sort of neck length most are not 30 caliber and none are as large as a RUM.

    It will work but will it work "fine" well.....

    As you point out, carbon ring, possible chamber erosion in the neck area.
     
  12. J E Custom

    J E Custom Well-Known Member

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    +1

    In addition to the short neck possibly not getting enough grip on the bullet, Proper Bullet alignment
    when loading becomes difficult.

    The recommended neck length is normally one caliber, although some necks are shorter than this and they still shoot well. (But most are less than 10% shorter than the caliber in length.

    Eventually brass and ammo will be available, so I recommend waiting and watching.

    J E CUSTOM
     
  13. 4xforfun

    4xforfun Well-Known Member

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    The ONLY concern I had was him doing it SAFELY!! Simply necking down and shooting could be dangerious. He would have at least a .09 headspace. Building a faulse shoulder would make this a safe endevor.
     
  14. 6x6 elk

    6x6 elk Well-Known Member

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    Thanks for all the advice, this forum has been extremely helpful since I'm new to reloading. I found some Remington ammunition that was $35 a box, so I'll shoot those and save the brass, and hopefully we will be seeing brass on the shelves in the future. I called Remington,and they don't have 300 rum brass being produced any time soon. They seem focused on loaded ammunition not reloading. Thanks again.