Throat erosion and double-based powders.

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Max Heat, Mar 24, 2012.

  1. Max Heat

    Max Heat Well-Known Member

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    I'm upgrading my Savage 110 7mm rem mag to a heavy stainless 7RUM barrel, and I shoot mostly light bullets (120gr Nosler BT's) that I figure will be sent out at well over 4K, using the maximum powder charge for the RUM. I'm prepared to accept a relatively short barrel life, but I have heard some say that double based powders such as Alliant (I've been using RL-19 in the mag) burn hotter, and therefore will erode the barrel faster.

    Is there any truth to this?
     
  2. brentc

    brentc Well-Known Member

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    Not sure if there is any truth to it. However, I have heard that double based powders have more lubricating properties due to the added Nitro glycerin, which purports to cause less fouling.

    There are a lot of variables in throat erosion. I think you'd have a hard time isolating the problem to only the use of double based powders.
     

  3. ovastafford

    ovastafford Well-Known Member

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    There is a write up somewhere on here on how ball powders won't erode your throat as fast as stick powders because they are less abrasive. Fiftydriver wrote about it I think. Maybe someone will chime in that knows which thread I'm talking about.
     
  4. Bart B

    Bart B Well-Known Member

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    120's from a 7mm Rem Mag leaving at 4000 fps?

    Max loads for 120's from that case leave at about 3300 fps at max safe SAAMI spec pressures. Not only will you get a very short barrel life, you may well shorten your own. Your case life will also be shortened to perhaps 2 loads per case.
     
  5. Outlaw6.0

    Outlaw6.0 Well-Known Member

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    Bart, the OP is re-barreling to 7mm RUM, which should help :D

    OP, I too have just started playing with Double based powder (RL-17). They sure do create more velocity.... anywho VV N-570 is next on my list in a 6.5WSM. I've been using ball powder (RamShot) in several cartridged for years, i'm actually really surprised how well it's treated my 6-284 (RamShot Magnum)... I'm not chasing the lands yet:D

    I wish I could help more, but that is the extent of my limited knowledge.

    Out of curiousity, why 120's??? TOF will be impressive but wind deflection should be terrible...gun)
     
  6. Bart B

    Bart B Well-Known Member

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    I saw that later, but thanks anyway for the notice.

    Both the Rem Mag and Rem Ultra Mag use virtually the same amount of powder for each bullet weight. So the difference is insignificant.
     
  7. Michael Eichele

    Michael Eichele Well-Known Member

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    The VV N500 series powders are alot like RL-17. Lots of velocity potential. I used to run N-540 in my 308 for 168-190 grain bullets and N-550 for the 208 AMAX. I used RL-17 a bit but to get top velocities with it the seating depth of the bullets was out of where I like to be. N-540 and N-550 allowed for less powder at similar velocities and the powder was a bit finer which let it settle better. 46.0 under the 208 AMAX allowed for 2615 FPS and could seat them deep enough to fit my 700SA with an extended magainze.

    I agree on the TOF and subsequent laser flat trajectory but you are right also about the windage sucking.

    Max, I realize you are prepared for 'relatively' short barrel life but do you know how short? I would be suprised if it went 100 rounds running 120's at 4000 FPS. Even if you had a 28" barrel. Her life will be not relatively short it will be downright non-existent. RUM case rifles (7mm-300) can last a good bit IF you don't hot rod them. You hot rod it, you pay the price.
     
  8. Outlaw6.0

    Outlaw6.0 Well-Known Member

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    BART,

    Maybe I misunderstood what you mean but, from the hodgdon site:

    7mm RM:
    120 GR. HDY SP Hodgdon H4831 .284" 3.230" 65.0 3095 45,800 CUP 68.5 3236

    7mm RUM:

    120 GR. NOS BT Hodgdon H4831 .284" 3.600" 85.0 3344 54,600 PSI 90.0 3536


    Same Bullet weight, same powder. 22 grains & 300 fps difference, did I miss something?
     
  9. FEENIX

    FEENIX Well-Known Member

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    Last edited: Mar 26, 2012
  10. Max Heat

    Max Heat Well-Known Member

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    First of, the RUM can handle 25% (or 25 grains) more powder than the rem mag, thereby adding around 10% more velocity to any given bullet, resulting in 25% more "hitting power".

    I suppose that most of those who do go ultra do so because they are looking for big bore size, and/or big bullet weight. But apparently I am one of those individuals who was blessed (or more likely, cursed) with the "need for speed" mentality (note my user name). I maxed out (actually, max + 1.5) on the mag at 75gr of RL-19, without my bolt going tight. Velocity at 15ft was 3680fps, + or - 5fps on 80% of the rounds fired. That probably equates to 3700 at the muzzle. Despite not having a tight bolt, I WAS very nervous firing those rounds.

    The one over-charge that I did have (not sure how it happened), gave me a reading of 3875 at 15', with a very tight bolt! The amount of RL-19 that my figures indicate would have been needed to achieve that velocity, is 83gr! It must have been a really compressed load. THAT put put a scare into me, so it was at that point that I decided to chamber-up to something that can handle that much (and considerably more) of a charge, without the bolt going tight. From THAT perspective, doesn't 4000 seem reasonable for the RUM, especially since the required charge would probably still be a good 10-15gr below the max capacity (100gr) of the RUM.

    And barrel burnout in only 100 rounds? Why do you think THAT low? The 220 runs similar/greater velocities. Albeit, it IS known to be a barrel burner, but with modern steel formulations, I'm thinking it should do 500-1000 rounds before accuracy goes out the window. I'm looking at the 7RUM that I'm building as the 220's "big brother".

    EDIT: Just like the 220 can basically "vaporize" prairie dogs, I want to vaporize ground hogs!
     
    Last edited: Mar 27, 2012
  11. Max Heat

    Max Heat Well-Known Member

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    None of the posted load data applies to the powder that I've been using in the mag (Reloader 19).

    Does anyone have any 7RUM data (max loads&velocities) for the 120NBT/RL19 combo?

    Or is #19 simply too fast burning for the RUM, even though the light bullets will spend LESS time inside the barrel than in the rem mag?


    Is there any 120NBT/RL22 data for 7RUM out there maybe??

    What about 100 grainers at 4 grand (or even higher?), if the 120's generate too much pressure for the 7RUM, at the target velocity, with ANY powder?

    You just gotta love how accurate those 7mm 120gr Nosler ballistic tips are though.
     
  12. Michael Eichele

    Michael Eichele Well-Known Member

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    Having destroyed a throat and creating heat checking out the a$$ in a 300 RUM in less than 70 rounds by running 180 grain pills at 3400 FPS is why I think the barrel life for the 7mmRUM will be so low running such 'hot rod' loads. I could be way off but having conversed with other 7mmRUM users and hearing their stories of rediculously short bore life while running top loads leads me to this opinion.

    Hope that helps.
     
  13. Bart B

    Bart B Well-Known Member

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    I was not wrong. Nor did I make an error. No mistake was made, either. Didn't even goof; not one tiny smidgen. But I sure was weak in being right................................ Shame, shame on me for mixing up the data on Hodgdon's web site. I'm probably the only person on this planet who's done that.

    Kudos to your for noticing. Excuse me while I find a rock to slither under..........
     
  14. Bart B

    Bart B Well-Known Member

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    My calculations for barrel life with a 7mm barrel burning 85 grains of powder is rather short. With bore capacity at 38.5 grains, 85 grains is about 220% overbore. Barrel life will be about 600 to 700 rounds.