7 mm SHERMAN SHORTMAG vs 7 SAUM

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by elkaholic, Jun 27, 2015.

  1. elkaholic

    elkaholic Well-Known Member

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    I am in the process of getting a 7SS together, thanks to the gunsmithing talents of a certain forum member from Dillon Mt.:D I hope to be slinging lead in the next couple of weeks at which time I should have some real world data. In the mean time, I wanted to introduce the cartridge and what I am trying to accomplish. First of all, it is simply a necked up version of the 6.5 SS which has proven to be a very good performer.
    Here are a few comparisons between the 7 saum and the SS and what I feel are improvements over the saum. The SS is .075" shorter oal. It is .095" shorter at the neck shoulder junction which determines where proper bullet seating depth starts. It has a .020" longer neck than the saum. It has a 40 degree shoulder and less body taper keeping case stretching to a minimum. The shorter powder burning column is more efficient. A 168 Berger seated to the base of the neck will have a coal of 2.870" to the lands so the round will cycle through much shorter magazines without loosing case capacity. The case capacity is right at 72 grains, but the USEABLE capacity is likely slightly more than the saum unless the saum is single loaded with a longer than normal throat, therefore; coupled with the shorter burn column, I expect velocity to be slightly higher than the saum. We will see:) I expect to be able to exceed 3100 with the 168's and 3000 with the 180's. Questions, comments, or flag throwing are welcome:D.........Rich
     
  2. MudRunner2005

    MudRunner2005 Well-Known Member

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    Can't wait to hear more results Rich. Definitely keep me updated.
     
  3. bigngreen

    bigngreen Well-Known Member

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    Here's a little teaser, got me a little a Krieger 5R, #4 contour barrel and JGS reamer together this evening and we produced a 7mm Sherman Short!!
    IMG_20150627_195030188.jpg

    IMG_20150627_195135577.jpg
     
  4. CanuckR

    CanuckR Member

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    TAG
     
  5. elkaholic

    elkaholic Well-Known Member

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    I also omitted another very important plus. BARREL LIFE! With a .331" neck and 40 degree shoulder, the SS will contain the flame point within the case neck much better than the saum, or anything else in its class. This should cut down significantly on throat erosion.......Rich
     
  6. Ridgerunner665

    Ridgerunner665 Well-Known Member

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    The 280 AI is right there with the 7mm SAUM in regards to case capacity...the Ackley has a pretty good neck too, I forget the exact measurement right now but I thought it was .34" ish...case capacity in mine is 74 grains, with 168's seated to mag length (~3.40" or so in my rifle) usable capacity is a tad over 65 grains...

    I'm not trying to belittle your round...sounds like a really good one, really...just wondering if the only difference between it and the Ackley is long vs short action?
     
  7. elkaholic

    elkaholic Well-Known Member

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    No offense taken at all! I have a 280 Sherman that is similar to the a.i. with a little more capacity, so I know what you are saying. The main difference is that it is a short action, and short enough to cycle with long bullets which the others will not. Also, because of the very short burn column, it is more efficient than the A.I., or the Sherman for that matter. I can exceed the velocity of the a.i. with less powder, and in fact it will equal the velocity of the long action Sherman. I say this based on what it does in both of the 6.5's, so the proof for the 7SS will be in the field test soon to be.......Rich
     
  8. Canadian Bushman

    Canadian Bushman Well-Known Member

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    Rich,

    What case will you be forming the brass from, and how involved will it be?
     
  9. elkaholic

    elkaholic Well-Known Member

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    I use Norma 7 saum or 300 saum. You can use RP brass but I think Norma is better quality. The process involves pushing the shoulder back with a shortened 7 saum die, trimming to length, turning the neck, and fire forming with c-o-w. you can easily turn out 100 perfectly formed brass in a day......rich
     
  10. Canadian Bushman

    Canadian Bushman Well-Known Member

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    I know you are still in the development stages, but do you feel the accuracy will be close to the potential of the 284 win?
     
  11. elkaholic

    elkaholic Well-Known Member

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    I can not think of any reason why it wouldn't be AT LEAST as good because it has a much longer neck and you could load it down to mild pressure and still outperform a 284 by a bunch. This is the thing about this cartridge. It is so efficient that top velocity is possible but not necessary to still get great performance and even better barrel life. (this is based on the performance we have seen in the 6.5 version). There is no reason to believe that the 7mm will not be equally good......Rich
     
  12. Canadian Bushman

    Canadian Bushman Well-Known Member

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    Or just load it up with a really heavy bullet?
    Im really liking the sound of this, especially if berger ever realeases that mystical purple unicorn of a bullet!
     
  13. bigngreen

    bigngreen Well-Known Member

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    A 180 hybrid seated at lands at 2.9 Coal.:D Savage model 11 dbm. The bearing surface just intrudes into the shoulder area with the 180, a 168 is perfect but I have a throater and after I get Riches built I'll get around to building me one but I'll throat it for a full 3 inch overall which should work well with the 180 Hybrid even in a mag.
    IMG_20150628_201515548.jpg
     
  14. royinidaho

    royinidaho Well-Known Member

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    Hey.... U guys are tearing me up (as in ripping vs crying like a baby:))

    As Mr. Dillon MT knows I'm between barrels on one of my barrel eaters and am licking those wounds sufficiently to not want to do that again. The remorse is pretty much like losing a good dog.....

    Until now I was pretty much settled on a 7 300 Win Mag after going cheap are seriously considering rechambering one of the shot out barrels to 270 WSM.

    Then here comes this 7ss..... Only lacks a little of the velocity of the 7 300 and if I could live with the 338 RUM vs the 338 Lapua I could most probably live with that, wouldn't cha think...:)

    In a moderate weight 28" 8 twist bbl it otta be decent for smoking critters deer size and below from a fairly decent distance.

    I have an everything ready to go except for a barrel, chamber and dies.

    Keep us posted on velocities but barrel life is the over riding consideration on this one.

    The two barrels gave up the ghost, one at ~ 900 and the second one < 600. The 7 300 has been known to get 700 w/o degradation but its uncharted beyond that AFAIK.

    PS: I'd be perfectly satisfied with the 168 pushing 3200. Just say'n.....