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The self limiting nature of Varget

Discussion in 'Ammunition & Reloading' started by Morpheus, Feb 19, 2015.

  1. Morpheus

    Morpheus Columbia Gorge Anyway, back on the farm.

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    I've been reloading for a few years, trying to find a solid .308/762 load. I've been sticking with Varget as it is very solid overall.

    One thing I've read and experienced myself is that Varget almost self-limtis when it comes to pressure. Having loaded up some fairly heavy loads (45.1 to 46.0 grains) I'm seeing no signs of pressure on the brass and everything is smooth.

    I've read about how people theorize that Varget just doesn't burn fast enough to over-pressure the round. Have other people seen this behavior?
     
  2. alphapygmy

    alphapygmy Yamhill County Active Member

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    I had similar experiences with 308 and Varget and also the 260 Remington using H4831SC. I've never been able to stuff it full enough to over pressure it, even in my 260AI.
     
  3. 308

    308 ΜOΛΩΝ ΛΑΒΕ ΜOΛΩΝ ΛΑΒΕ Platinum Supporter Silver Supporter

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    43.5 gr with 168gr BTHP Sierras is the sweet spot for me when using varget. It seems to match the Fed GM Match 168gr very closely.
     
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  4. Benchrest

    Benchrest The Desert Planet Well-Known Member

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    I've loaded Varget fairly hot behind 168gr SMKs and never had any signs of pressure.

    Never could get Varget to work for me.

    .02
     
  5. Morpheus

    Morpheus Columbia Gorge Anyway, back on the farm.

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    What is fairly hot? I've gone up to 46.1 grains in a .308. And still no pressure signs. I can't really get much more in there. Not that I want to, of course.
     
  6. Benchrest

    Benchrest The Desert Planet Well-Known Member

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    I'll look up the loads tonight - they were 46+.

    If I'm remembering right...
     
  7. Darkker

    Darkker Mesa, Wa Active Member

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    Stop believing in voodoo.
    First and most important, looking at your brass and primers as an indicator of pressure is about the dumbest thing you can do. VERY accurately calibrated copper crushers do NOT accurately report pressures over around the 50,000psi range, the industry has repeatedly proven and excepted this decades ago. Knowing that nugget, you think your very UN-CALIBRATED primers and brass will somehow tell you that you "don't have a pressure problem"?!! No.
    The alloy that was very common years back, and the reason most think "Winchester brass is good stuff" was Olin alloy C260, which was hardened to a tensile strength of around 85,000 psi. Guess what pressures you are ringing when that stuff shows head expansion?....

    Of the non-pressure testing methods, the chronograph is the best way to tell. The very tightly controlled chamber and bore/groove specs used for testing, will ALWAYS hold more pressure, thus have more velocity than any factory rifle. So if you are pushing faster than printed velocities, it is because you have higher pressures.
    From a bunch of work I did with a pressure trace in December, at least in the Creedmoor case; each additional 75fps is the result of an extra 10,000 psi.
     
  8. The Heretic

    The Heretic Oregon Well-Known Member

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    I have to agree with Darkker; brass and primers are not a particularly accurate way of detecting pressure that is too high, even less that pressure is at safe levels.

    I am an engineer, from an engineering family, and there is an old engineering saying; "if you don't measure, you don't know". I see people, including engineers, ignore this very basic axiom every day.

    Put a good calibrated strain gauge on that rifle, run your loads, and then tell me about the results.

    Don't guess, measure.
     
  9. Morpheus

    Morpheus Columbia Gorge Anyway, back on the farm.

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    Lacking the equipment you write about and using chrono speed as my only data driven guide, what would an all but flattering out of the speed mean to you?
     
  10. Darkker

    Darkker Mesa, Wa Active Member

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    I'm not following your meaning about a "flattering out of the speed", so not sure what you are asking.?
    From my Creedmoor testing, 75fps faster than posted data equals 10,000psi over.
    Here is a visual for you:
    This load had ZERO extraction, primer, recoil, ANY tell-tale that there was pressure problems. But you can see the powder began to run-away. Pretty nasty secondary pressure spike also...
    Screenshot_2015-01-31-15-00-18_zpsmopqcu83.png
     
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  11. Benchrest

    Benchrest The Desert Planet Well-Known Member

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    So stick to published specs :)
     
  12. Morpheus

    Morpheus Columbia Gorge Anyway, back on the farm.

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    Sorry for the quick cryptic message before. My initial question was about how Varget seems to hit a peak speed and just stop. You can't go over a certain point given the rate of burn for the powder in the case. Specifically for 308. I'm seeing speeds just plateau and not go any higher. These are withing +/- 10 fps of the powder's max speed according to their spec.

    This is what I've heard about Varget before, and wasn't sure if others had seen this same effect or not.
     
  13. Darkker

    Darkker Mesa, Wa Active Member

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    Now I'm following the general premise.
    It doesn't have a peak, the change just gets smaller. Many people don't shoot enough test rounds to get statistically valid numbers.

    For an example:
    If the load range is 38-45 grains for a given combo, with a velocity spread of 2,000 - 2,700 fps.
    Some would say that for every grain, you get 100fps; EXCEPT when I over-load to 46gr, I don't gain that 100fps.

    While the premise of 100fps per grain holds true, IN that operating pressure window; powder does not burn linearly to eternity. Each powder, in any cartridge, has it's "happy" pressure operating range. Outside of that, things don't play the same. Look at my Pressure Trace in the post above, that powder ran away when pushed outside of it's comfort zone. Look at the velocities associated with those pressures!!
    T2 was higher pressure that T1, yet slower. The rise time of a powder is where the work gets done, that part never moves much, so even with alarming pressures, velocities don't track perfectly.

    That is why, unless you are running a Pressure Trace, you can get into a heap of trouble quickly if you exceed published data; or try and "read primers" for pressure.
     
  14. Morpheus

    Morpheus Columbia Gorge Anyway, back on the farm.

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    My premise is that eventually you will not have enough time/space/air to burn the powder and you will just blow grains down the barrel unburned. Thus in that way some powders would end up self-limiting.

    I understand your comments about using a true Pressure Trace system. I would like to get one, and will put it on the list. Though, it isn't something in the budget right now.
     
  15. Darkker

    Darkker Mesa, Wa Active Member

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    Provided the burning rate is suitable for the application & operating pressure (not too low):

    You won't ever blow powder out the barrel due to incomplete combustion. Powder doesn't need ambient air to combust, it's molecule has everything it needs.
    More powder=more pressure.
     
  16. orygun

    orygun West Linn Bronze Supporter Bronze Supporter

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    While I don't have the knowledge or testing methods that Darrker does, I agree with this statement completely.
    One other variable is barrel length for published loads vs. your gun. Most manuals use 24", or even 26", for their test gun.

    Yesterday, for the first time in a few years, I was working up loads with a new bullet. This is before I load 400 rounds for an outing. The case, primer and powder were what I'd used before. The bullet manufacturer listed 58.3gr as max with their combination. I'm using a different case with a slightly larger internal volume than the bullet maker used for testing. Another bullet manufacturer (yeah apples/oranges) lists up to 62gr of powder as max and I have used 61 without problems.
    I set up 4 charge weights to test. 58, 59, 60, & 61gr.
    Shot over the chrono, 58gr was 100 fps behind factory ammo. 59gr, gained 100fps, matched factory ammo and had a low extreme spread and SD. 60gr only gained 25fps. The ES was whacky and the SD tripled! 61gr gained 60fps over the last loading with ES and SD a little better, but still high. At this point velocity matched the loading manual, from a 4" shorter barrel! The groups for the two highest loads really opened up. Before I shot the last batch I knew I was pushing things...
    Long story long, none of the primers looked any different. The bolt fed and extracted every case just like the rest. No "signs" of high pressure could be seen in the case or primer. They all looked exactly the same. I've not yet miked the cases, but will because I am curious to see if that can confirm what I already know.
     
  17. orygun

    orygun West Linn Bronze Supporter Bronze Supporter

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    Was this 5 shots of the same charge weight?
     
  18. Darkker

    Darkker Mesa, Wa Active Member

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    That was actually averaged over 15 shots of the same load.
     
  19. Darkker

    Darkker Mesa, Wa Active Member

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    The trace with the 5 - shots, are the same load, yes.

    The 75fps/10,000psi was the average of 15.
     
  20. jluck

    jluck Really,Really, Close to Newport Oregon 97365 Voted #1 Member

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    My premise says... More often times than not a rifle will shoot better groups long before "maximum speed" or overload is achieved. Find the fastest load within reasonable published data that shoots the tightest groups. I will always believe in hitting my desired POA slower than miss faster. YMMV.
     
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