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Thread: Customizing Casings for .375/358 Norma Magnum

  1. #1
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    Default Customizing Casings for .375/358 Norma Magnum

    My rifle is a .358 Norma Magnum that shoots a .375 bullet. It loads a lot more powder than a standard .375 and speed is also a lot more able. Grouping and accuracy is excellent and better that the .375 H&H.

    Problem: No commercial Cartridges or casings.

    Does anyone know how the process works to "fire-form" casings. I need to know about the amount of powder to use when this is done. Any advice welcome.

  2. #2
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    Default Fairy tales...

    Quote Originally Posted by Dif Botha View Post
    My rifle is a .358 Norma Magnum that shoots a .375 bullet. It loads a lot more powder than a standard .375 and speed is also a lot more able. Grouping and accuracy is excellent and better that the .375 H&H.

    Problem: No commercial Cartridges or casings.

    Does anyone know how the process works to "fire-form" casings. I need to know about the amount of powder to use when this is done. Any advice welcome.
    It seems you have a nice wildcat there but it isn't anything magical.

    There is no fireforming required if the chamber is made correctly, you just neck up 358 Norma brass with the 375/358 dies with a tapered expander. This is actually a very good case for the 375 but with the price of brass it isn't practical, it is available and I have some on hand. It will not exceed the ballistics of the H&H by any measure (giving a maximum velocity of 2600 fps from 24" barrels), nor is it more accurate given good rifles. It's only advantage is it's use in shorter actions.

    I bought a very nicely made custon rifle made on a good Mauser action for this caliber back about 1985 and used it heavily for a number of years.

    The choice of powder for this one is the same as for the 375 H&H, RL-15, H4350 and those similar in burn rate. Powder charge will start at about 70 grains of RL-15 with 270 grainers and 70 grains of H4350 with 300 grain bullets. If you are new to handloading I would advise against loading this without assistance. By your post I'd say you need some assistance. I can inundate you with details and data for the caliber if you wish, but that would best be left to a PM as most here won't be interested.

    If your in the Fairbanks area e-mail me and we can link up, I can load for the caliber and would be glad to help. Do you have dies? If not I have dies here we can use. If you would like I can load up some loads for you using Norma 358 brass I have. I'd like to examine the rifle first. Let me know and good luck.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



  3. #3
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    Default Oops!!

    Dif,

    I just check your location, you're in RSA, huh?

    Well in that case things are different. You may not have access to 358 Norma brass and need to use the H&H brass. That will require some cutting to about 2.6" and then run into the die. We will need to use a fire forming load. The shoulder of the H&H is enough to headspace for fireforming with a bullet. When cutting the case don't trim to required length until after firing. 2.6" or so will do, it will shorten when fireformed. When you run it into the die for the first time, back the die off so it doesn't set the shoulder back. This will make a tight closure and good headspace. Use only new brass if you can.

    You will likely be using the Somchem powders. I have used them in RSA with a PH friend of mine. I have notes and a brochure from Somchem in my note book but going from memory now I recall using S335 for the lighter bullets, which would be best for fireforming, and S341 and S355 for the regular loads for both 270 and 300 grain bullets.

    I guess you won't be stopping by but I'll be in your neighborhood later this year. I always like to do some loading with the Somchem powders when I can. We don't get those over here. Good luck with the project and let me know how it goes.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



  4. #4
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    Default

    Dif,

    The unfired 358 Norma brass I have here, when necked up to 375 holds exactly 90.0 grains of water. I have in my notes the 375 H&H case holds 94.0 grains of water. This means we will need to reduce loads for the 375/358 Norma four grains to start.

    I have in my notes for the 375 H&H with the 300 grain PMP bullet and CCI-250 primers a load of 70.0 grains of S341 gives 2544 fps. You should start at no more than 64.0 grains of S341 with the 300 grain bullet.

    I have a load of 72.0 grains of S365 and the 300 grain PMP bullet gives a velocity of 2560 fps. This powder is closer to the burn rate of our 4350 and I think it works better than S341. Again, reduce loads by 6 grains to start with the reformed H&H brass.

    My friend runs the Meletse Camp up north in the Waterburg mountains. I've hunted that area a lot and really like the rugged hill country. Good luck.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



  5. #5
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    Default

    Hi Murphy, I'm sitting here with a nice 375 H&H barrel but no long action for it so have been thinking of the 375 Ruger for it but was also kiccking around the 358 Norma case and came upon your post. I would love to get any info on it that you may have. I am affilated with North Fork Bullets so have the best money can buy but just need to build the rifle to shoot them. What is your take regarding the two cartridges? I think the 358 would be better suited to the Mauser. Have a 8mm Mauser AI and 8mm-06 AI that are both pretty wicked. They will both kick out the 180 gr. Barnes TX at 3075 and 3160 respectively but want the 375 to take to Africa and as a alternate rifle for Alaska. My direct email is archeratlrg@aim.com" Thank you for any input.

    LeRoy

    Roy's Custom Gunstocks
    (970) 819-9878
    Last edited by archeratlrg; 12-06-2012 at 19:03. Reason: needed to add email address

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