A .300 MAG Wildcat?

Discussion in 'Reloading' started by kc, Sep 5, 2011.

  1. kc

    kc Well-Known Member

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    Have you ever known of a gunsmith who used a .300MAG case necked it to a .7mm Bullet?
    I have no information or history. Just a wild idea.
    I was thinking it would ba a smoker.
     
  2. kc

    kc Well-Known Member

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    Guys I think I pulled a Dum Dum is the a 7mm Ultramag? I have no info.
     
  3. Broz

    Broz Well-Known Member

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    No it is not a 7mm Rum. It is a 300 Win Mag simply necked down to 7mm. Good brass is available by necking down and dies I use are redding 300 win with a bushing change. This caliber has also been call the "7mm practical" some of us are very fond of it.

    Jeff
     
  4. BUNDUKI

    BUNDUKI Well-Known Member

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    kenny jarrett calls it the ".284 jarrett" this is what he has to say about it on his site.

    "We were amazed that the .300 Winchester Magnum had never been reduced to 7 mm successfully. The wheels really began to turn wondering exactly what the volume of the case would be. We designed a different case taper, then used our traditional 35 degree shoulder along with a lead angle in the throat to accommodate 140 and 160 gr. bullets. We had a reamer made and proceeded to build the .284 Jarrett! After the case fire forming was completed, we did comparisons with the other big sevens to see where ours fit. We checked all of the cases by water volume and this is what we came up with: (volume to base of neck)

    7mm Remington Magnum ..........73.5 gr. | 7mm Weatherby Magnum ..........78.0 gr.
    ..284 Jarrett ................................85.5 gr. | 7mm STW ................................98.3 gr.

    It’s interesting to note where we are volume wise: 12 gr. greater than the Remington Magnum and 13 gr. less than the 7mm STW.

    The next step was to shoot this thing! Of foremost importance to us was its accuracy. If it’s not accurate, the velocity doesn’t matter. The cartridge responded well to a variety of powders and without effort we were under our half minute accuracy with velocities appropriate for this case capacity. Our testing produced the following results:

    140 gr. Nosler bullet.................................... 3450 to 3500 f.p.s.
    ..150 gr. Nosler bullet.................................... 3350 to 3375 f.p.s.
    ..160 gr. Nosler bullet.................................... 3250 to 3300 f.p.s.

    These velocities are identical to a 7mm STW with a lot less powder. Even though all the 7mm cartridges are listed overbore, the question is how much overbore can you stand and still have a dependable cartridge? I do know the velocities shown are the absolute maximums for 7mm bullets, regardless of how much powder you use. The Mexican standoff: the bigger case won’t give you any more, and a smaller case won’t give you as much. This is the reason, for all the 7mm fans, we have to max out the 7mm bullet. It rounds out our performance cartridge line and gives us a big 7 that meets our accuracy criteria while producing predictable velocities. In an emergency, a Weatherby cartridge can be used in the .284 Jarrett, but I don’t recommend reloading them because the neck will be too short. Put a .284 Jarrett in your battery soon!"
     
  5. kc

    kc Well-Known Member

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    Thank you. you answerd all my questions.
     
  6. Edd

    Edd Well-Known Member

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    The person who wrote this didn't really measure them. Because of that, I wouldn't take any of those numbers as factual without confirming them.