7mm SAUM Wildcat!

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by redneckclimbing, Feb 12, 2012.

  1. redneckclimbing

    redneckclimbing Well-Known Member

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    Hey Everyone-

    I am going to build a long range hunting rifle in some sort of 7mm. I am set on compmnents: Lawton 7000 SA, 30" Kreiger 1-9 twist, AI stock. My dillemma comes with the 7SAUM and loading 180 Berger's long. (I want to use an AI stock and magazines and obviously they won't work this way.)
    I had also noticed that a .284 Shehane will do basically the same velocities but is even a tad longer when loaded long. This got me thinking wildcat. My idea was to take the proportions of a 6mm Dasher and push them out to a SAUM case.
    When I did these calcs. I found some interesting things:
    - This gave me almost identical volumes to a .284 Shehane
    - The start of the shoulder was only slightly shorter than a standard SAUM

    So, I thought why re-invent the wheel? Keep the lower (below the shoulder) part of the case the same, and put a 40' shoulder on it. With this combination it should have a slightly larger capacity than the Shehane but not much. This smaller volume should be more efficient than the SAUM or WSM. I am hoping that with about 56 grains of H4831sc it will consistently reach the 3000-3050 fps velocity node.

    Advantages:lightbulb

    - This will easily fit into an AI mag. with a 180 Berger loaded long
    - with the 40' shsoulder I think that t will give slightly better vels. with similar charges as the Shehane
    - With a similar powder load to the Shehane I was thinking that the barrell life should be similar (everything else being the same).

    I have drawn up a reamer for Mr. Kiff but am needing some suggestions on some things I didn't really know. (the question marks on the print) I was also wondering if someone could run this through QUICK LOAD and see what it spits out.

    I also have not had a chance to measure any bullets yet so if anyone knows the bearing surface lengths of some bullets and could post them that would be great so that I can finalize the freebore length. As you may notice this is basically a SAAMI chamber with a 40' shoulder and a slightly tighter neck.

    Please let me know what you think!:cool: View attachment 6482

    Here is a copy of what I have so far.
     

    Attached Files:

    Last edited: Feb 13, 2012
  2. webs

    webs Well-Known Member

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    Why don't you want a long action?
     

  3. redneckclimbing

    redneckclimbing Well-Known Member

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    Valid point, I was, more than anything, trying to make a more efficient cartridge.
    The ultimate goal here is to get WSM velocities while using the same amount of powder as the Shehane. The fact that all this would fit in a SA is just an added bonus!
    Also, I forgot to mention, the body has also been shortened .100 this should give an overall length of 2.80" or so. And about 67.5 grains of H2O capacity.
     
    Last edited: Feb 13, 2012
  4. redneckclimbing

    redneckclimbing Well-Known Member

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    Sooo, I thought why not straighten out the case a bit? This reamer would give the same body taper as a WSM and add about a 1.5 grain of H2O cap. Has anyone had any problems extracting their WSM's or does anyone think this could cause a problem?
     

    Attached Files:

  5. Mikecr

    Mikecr Well-Known Member

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    I don't know anything about your action, but I think the cartridge is a great choice(minus available brass).
    And I'll check with the ole lady, but I'm thinkin you should consider length AND girth for your magnum diameter cartridge.
    Otherwise you may not reach the desired potential before extraction issues.
    Be sure you have sufficient barrel steal around the chamber(magnum barrel tenon) w/resp to a working design(like Savage WSM barrels).

    Also check to be sure you can eject from your port.
    While a SAUM is shorter than other magnums, it's not a short cartridge.
     
  6. 4bycamper

    4bycamper Well-Known Member

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    +1

    We shoot 7mm saum and 270 wsm.
    Don't know what your mag length is but I can give you some ideas.
    My 7 saum 160 AB is 2.952 col, Browning wsm action.
    ..................168 VLD 2.938 col.

    MY 270 wsm 150 AB is 2.905 col, Winchester crf action.

    My gs did quite a little bit of work to get the 160 AB to fit in the sa Browning mag. He lengthened a couple of mags .125 each and notched the ejection port to eject a loaded cartridge. If I had to do it again I might choose a Browning long action.

    Good luck with your build.
     
  7. calinb

    calinb Active Member

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    Another reason for the short action is detachable box mag capacity. The long action AICS mags only hold 5 rounds, maximum. The only exception that I know about is the Accurate-Mag 6-round double stack. Please let me know if you know of a source of higher capacity long action mags. The Accurate short action magnum mag (00100-0008) holds 7 rounds. This is a 40% improvement in capacity over a 5-round long action mag!

    redneckclimbing:

    I've been considering doing a 7mm long range rifle project on the cheap. Though it's not very popular for custom work, I'd like to use a Ruger M77 Hawkeye as the platform. I was even considering using the Gunsite Scout Rifle and avoid the expense of DBM bottom metal, but I don't feel comfortable with a short action for long 180 gr. Berger (or Even 162 gr. Amax) loads. Even with a max COAL of 2.980 inches, which seems to be about as long as you can feed with Alpha mags and similar, it's just too close for comfort for 284 Win, 284 Shehane, 7mm SAUM, 7mm WSM, or 7-08. Quickload helped me to reach this conclusion. Seekins has a 3.1" COAL WSM solution, but it's not AICS and it's only for Remington actions.

    So I'll machine my own bottom metal, if I have too, but your wildcat might permit me to save some time and money and use the Ruger GSR after all!

    I have Quickoad and Quicktarget. We could work together on this. Let's exchange PMs and email addresses.

    -Cal
     
    Last edited: Mar 2, 2012
  8. calinb

    calinb Active Member

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    I am worried about 40 degrees feeding from a mag. 35 degrees is about the industry max and even it doesn't feed terribly well.

    I'll run the the resulting case capacities through Quickload, when I get a chance.
     
  9. calinb

    calinb Active Member

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    I did some case capacity calculations and Quickload runs on several candidate parent cases and I think I may have found a simple wildcat solution to my problem (feeding 7mm 180 gr Berger VLDs from a short action mag).

    The 7mm WSM seems to be the least case capacity-challenged of the short action 7mm cartridge bunch (by a very slight margin) so it would be simple to just push back the 7mm WSM shoulder by 0.100" and get some COAL breathing room. I'll call it the 7mm WSM LRMF (long-range mag-fed). I think the chamber free bore and throat probably need appropriate adjustments too, to make sure the VLDs can touch the lands.

    My goal is 2950 fps from a 28" barrel. Here are the Quickload results of pushing the 7mm WSM shoulder back 0.010" using readily available powders:

    Cartridge : 7 mm WSMLRMF
    Bullet : .284, 180, Berger M T VLD G7 #28502
    Useable Case Capaci: 67.267 grain H2O = 4.368 cm³
    Cartridge O.A.L. L6: 2.980 inch = 75.69 mm
    Barrel Length : 28.0 inch = 711.2 mm

    Ramshot Magnum (Big Boy)-------------102.2 3035
    Vihtavuori N560----------------------------99.8 3033
    Accurate MAGPRO-------------------------100.1 3030
    IMR 7828----------------------------------104.3 3019
    IMR 7828 SSC------------------------------98.6 3019
    Alliant Reloder-22-------------------------100.1 3000
    Winchester WXR--------------------------102.8 3000
    Alliant Reloder-25-------------------------105.0 2997
    Vihtavuori N570---------------------------105.0 2988
    Alliant Reloder-19---------------------------97.2 2957

    Pushing the neck back 0.100" costs 5.9 gr. H20 but 0.9 gr. H20 could optionally be "recovered" by reducing the case taper to 0.010" (or "spend" the taper reduction to push the shoulder back another 0.030).

    From my experience, just pushing a short magnum case neck back 0.100" is a fairly easy task in forming new brass, though it's about the limit of what I've attempted to do.

    A wildcat seems like a lot of trouble for only 0.100" or 0.130" of COAL relief, but I think my goal is marginal without it. Unless extraction problems are anticipated, it seems like the additional 0.030" COAL increase from trading off the cartridge taper is worthwhile. Every little bit helps in this application.

    In fact, I'd rather have 0.150" to 0.200" of COAL "guardband," which may be possible with a further reduction in case capacity. Quickload seems to be a touch pessimistic with many of these long range 7mm loads and I was limiting QL to only SAMMI max. pressure. ;)

    So maybe I can rework the Ruger M77 308 Win bolt face and extractor and use the Ruger GSR as a platform after all.

    Comments, suggestions, or ideas?

    Thanks,

    -Cal
     
  10. calinb

    calinb Active Member

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    I'm new to reading these prints too, but I think the question mark boxes are for the throat angle and length (they are geometrically dependent on each other so, technically, it should only be necessary to provide one or the other of the values). The first question mark box is for the throat angle extending into the rifling (the taper that begins after lead section, which is straight in most chambers).

    Downloading the prints from SAAMI, I see that the throat angle is 1.5 degrees (1 degree, 30 minutes) for the WSM cartridges and 1 degree for the 7mm SAUM. The second box that your marked with a question mark should be the length of the tapered throat section that ends at the fully rifled bore. SAAMI prints seem to specify only the throat angle and not the length of the angled throat section.

    My latest results look good for short-chambering in 7mm WSM by 0.20" and modifying a full length sizing die to push a 270 or 300 WSM case shoulder back 0.162, if that much push back can be done cleanly. Quickload says it should slightly outperform the 284 Shehane and achieve 2950 to 3000 fps from a 28" barrel. I'm not so much interested in efficiency (requires 2.5 to 3 grains more powder than the 284 Shehane to match the same velocity with heavy bullets) as mag-feeding and more easily manufacturable brass.

    I don't see much interest in this thread so I might need to move to another forum. I certainly need to run my ideas past people more expert in the art than I!

    -Cal
     
    Last edited: Mar 3, 2012
  11. redneckclimbing

    redneckclimbing Well-Known Member

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    The dies I ordered from Spencer Tool & Grind left today and I have some brass waiting at the house for them. When I get a couple of them finished I will let you know what the case capcities work out to.
     
  12. redneckclimbing

    redneckclimbing Well-Known Member

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    Cal-

    Is there any way to know if the amounts of the different powders you ran will actually fit in the case? Also, if it is not too much trouble could you run Hodgdon 4831sc through there, I would appreciate it.

    Thanks,

    Travis
     
  13. Skyking

    Skyking Official LRH Spponsor

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    I just finished up my 7saum with a 35* shoulder. I end up using the Berger 168 vld and got them going 3160 fps with Retumbo. 4831sc had way to much pressure. H1000 was better.

    Here is more info on it. Bighorn 7saum Thunderbeast 30p-1!! - Sniper's Hide Forums

    Let me know if I can help.
     
  14. calinb

    calinb Active Member

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    Estimating accurate case capacities is a bit of a problem. Quickload doesn't really help and I always measure my actual cases by weighing them with and without water. For estimates of my hypothetical case, I used this calculator:

    http://kwk.us/cases.html

    It's probably best to input the numbers from an actual known capacity parent case for a baseline. Then "modify" the case in the calculator and work with the predicted capacity change, relative to the original case capacity.
     
    Last edited: Mar 27, 2012