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Thread: A couple of questions...

  1. #1

    A couple of questions...

    Today I tried a few loads out, using privi brass, and n550 powder. I tried 2 different bullets, Nosler BT's and swift Sciroccos, both in 150gn. Both were seated 10thou off the lands which gave slightly different COL due to the different shape of the bullets.

    The Noslers shot really well, no pressure signs right up to max load.

    The sciroccos showed slight pressure signs (extractor marks) at a lower charge, and continued to show pressure signs as charge increased, groups were good.
    One case blew a primer with a medium load and one primer leaked on tha max load. In terms of cases being tight the max loads were no worse than the lower charges, same for extractor marks.

    So my first question is: why would 2 bullets of the same weight and same jump show different pressures?

    And my second question is has anyone had problems with once fired privy brass, particulaly loose primers?
    I should point out that most of the brass was unfired and had original primers as I had just pulled the bullets. only a couple had been fired once before, one of which blew the primer out, the primer that leaked was an unfired original.


    I obviously won't be using this load again even though it shot quite well, can anyone explain the differences?

  2. #2
    different diameter?
    even a small difference between manufacturers can make a big difference in pressure

    I happened to be sitting here having a clear up:

    interlocks - 0.2780
    Speer HP - 0.2785
    Nosler Partition gold - 0.2775
    Swift Scirroco - 0.2785

    combine that with different COL and Ogive shape and you have different land/bore contact times

    sure that could make all the difference

  3. #3
    The scoroccos are about .0002 wider, maybe you are right...

  4. #4
    Quote Originally Posted by Tom D View Post
    ..I obviously won't be using this load again even though it shot quite well, can anyone explain the differences?
    Tom. No, I can't explain the difference. However I have a couple of comments. I tried 130 gr Scirocco in my 260 Rem some years ago.

    6.5mm/.264 Caliber - Rifle Bullets - Scirocco II - Bullets without equal!

    I couldn't get a load I was comfortable to take stalking, however some of the tests were very impressive, but I couldn't get them to work consistently. Secondly, they were very expensive then and I am sure they are even dearer now. If I was to try them again, I would use the best brass (Lapua) I could lay my hands on too. Regards JCS

  5. #5
    Quote Originally Posted by Tom D View Post
    The scoroccos are about .0002 wider, maybe you are right...
    Tom. Have you checked the relative length of the bearing surfaces? Regards JCS

  6. #6
    Quote Originally Posted by Tom D View Post
    So my first question is: why would 2 bullets of the same weight and same jump show different pressures?
    Different shapes. Different bearing surfaces. Different friction and resistence to movement. Resulting in different burning profiles, and different pressures. Consider a VLD type bullet, elongated with a short bearing surface. Now consider the bearing surface on a fat round-nosed bullet.

    Quote Originally Posted by Tom D View Post
    And my second question is has anyone had problems with once fired privy brass, particulaly loose primers?
    I should point out that most of the brass was unfired and had original primers as I had just pulled the bullets. only a couple had been fired once before, one of which blew the primer out, the primer that leaked was an unfired original.
    You mean the primers were loose after firing, not before? If so, that is a clear warning sign of an excessive load.

    -JMS

  7. #7
    Quote Originally Posted by jcampbellsmith View Post
    Tom. Have you checked the relative length of the bearing surfaces? Regards JCS
    I agree. But bearing surface is less important than bullet material/hardness until you get to heavier loads.
    A chronograph would have been interesting. Using brass of the same LOT and 'age' would have been the way to do go instead of 'mixed' brass. Adds a variable which, in this case, raised yet another question.~Muir

  8. #8
    I agree with that Muir, it would have been nice if all the brass was the same, having said that one of the loose primers was the original unfired case with original primer, the other was a once fired one...

  9. #9
    Update:

    I was chrono'ing some other loads the other day and after I had finished there in the box was one of the scirocco loads that I had neglected to fire after having the pressure signs. I fired it over the chrono and it promptly blew the primer. The speed was interesting, the same weight of powder pushes a 150gn nosler BT at 2812Fps. This one scirocco achieved 2860 so I will experiment with a reduced load and see if i can get them shooting.

    It would seem that the increased resistance and therefore higher pressure provided by the scirocco has translated into more speed. Makes me glad I bought the chronograph, its certainly a handy thing. What would otherwise have been a lost cause may in fact be a good bullet that is more economical to run than the nosler, all be it by just a few grains.

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