.300 Win mag to .300 Ultra mag

Discussion in 'Gunsmithing' started by Boman, Mar 24, 2008.

  1. Boman

    Boman Well-Known Member

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    I'm wondering what it takes to turn a rifle chambered in .300win to a .300ultra? As far as I can tell they both use the same twist in barrels and both use magnum sized actions. So my guess is other than getting it reamed to the new cartridge you'd need to open up the magazine and do some work with the feed rails? Please help with what needs to be done and what am I looking at for price.

    Question is if you had a .300win mag that shot great would you make the change? I've got a few .300win's and want something different.
     
  2. Jim Oliver

    Jim Oliver Well-Known Member

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    Answer: Only if you are willing to endure a bit more recoil, spend a bit more on powder and get about 150 fps more velocity (depends on your barrel) for your trouble.

    The 300 RUM magazine box is wider than the 300 Win box and the follower is different. Your 300 Win box/follower "might" work, but with reduced magazine capacity.

    I have both the 300 RUM and 300 Win----for the hunting I do (400 to 500 yards), there isn't enough difference to justify the change.

    My two peso's.......

    Cheers,
    Jim
     

  3. elkhuntinguide

    elkhuntinguide Well-Known Member

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    I had this done on a Remington 700 300 Win Mag. My smith changed the barrel with a new barrel. Replaced the box, spring and follower. He also opened up the feed rails a bit and all works fine. I really enjoy shooting the ultra and am very happy I had this done. Overall cost was around $220.00 for everything. Love the flat shooting long range shots. Killed my mule deer in 2007 at 873 yards. Ranged with a Swarovski Guide. Good luck.
     
  4. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    This conversion can range widely in complexity depending on the receiver your using. For a Rem 700, its pretty easy. As mentioned, open feed rails slightly for the fatter case, install a Wyatts 3.820" mag box. I have never had to replace the follower or spring on the Rem 700 to make them work.

    Other receivers can be alot more work so it just depends on what you have to build on.

    Kirby Allen(50)
     
  5. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Jim Oliver,

    Your 300 RUM only gets you 150 fps more velocity then your 300 WIn Mag? What bullets are you using and what barrel length? From what I have seen, your either loading the Win Mag up very hot or loading the RUM very mild.

    A fast 300 Win Mag will get you 3100 fps with a 180 gr and right around 3000 fps with a 200 gr bullet. On average.

    A 300 RUM will easily do 3300 fps with a 180 and some will even push 3350 comfortably. And the 200 gr bullets will usually always break 3200 fps in any barrel of at least 26" in length.

    In fact, a 300 RUM will generally drive a 220 gr bullet to nearly the same velocity as the 300 Win Mag will drive a 180 gr bullet.

    Now if the barrels are short, this will greatly handicap the big RUM. Also, if your using lighter bullets, the advantage will be smaller as well.

    Just curious on what your using to only see a 150 fps advantage with the RUM. Not a flame in any way, as we all know, some barrels are fast, some are slow so this could certainly be possible but it is not the norm comparing these two chamberings.

    Take care,

    Kirby Allen(50)
     
  6. phorwath

    phorwath Well-Known Member

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    Rechamber or New Barrel?

    In completing this conversion are you gunsmiths saying you would simply rechamber the existing 300 WM chamber/barrel to 300 RUM, or are you talking about replacing the existing 300 WM barrel and chambering a new barrel to 300 RUM?

    How would one rechamber an existing 300 WM to 300 RUM and ensure that the 300 RUM chamber remains concentric with the bore? Is this an issue worthy of concern? :confused: If so, how are those concerns addressed while rechambering? Thanks for any insights provided.

    phorwath
     
  7. Jim Oliver

    Jim Oliver Well-Known Member

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    Hi Kirby,

    In my 300 RUM I have gotten the 3350 fps that you mention with the Nosler 180 Bal Tips, using Retumbo and other powders, without straining anything.

    My purpose in using the lower number and the "depends on your barrel" qualifier was to not over state the advantage of the RUM. The question asked was about rechambering the present barrel, which is an unkown quantity.

    Just call me cautious.......

    Cheers,
    Jim

    Kirby, just for grins, I checked some of my loading books; some actually show less than 150 fps difference between the two cartridges, with the same bullet weights.
    Who would'a thunk it??
     
    Last edited: Apr 1, 2008
  8. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Jim,

    Thanks for clearifying, makes sense and I agree.

    Got to love those loading manuals. Ihave seen many that said the 243 and 6mm Rem are the full equal of the 6-284 in velocity!! Like ya said, go figure.

    Thanks for taking the time to explain your comments and I agree there is nothing wrong with being conservative!!!

    Kirby Allen(50)
     
  9. HarryCallahan

    HarryCallahan Well-Known Member

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    I agree with phorwath, I can't see how you would rechamber the existing barrel to RUM, the pilot won't even touch the throat until you were halfway thru the job. Reamers will find their own way which is usually center but given what's acceptable for runout I wouldn't try it.

    My personal experience shooting and loading for the 300WM, 300WBY and 300RUM, all in a 26" barrel, is that the 300 Weatherby generally performed as well as the 300RUM with 180gr loads with less powder and kick. I would say if you want something new, try the 300WBY IF your magazine length limitation would support it, many won't and you'll be into more work opening it up.