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Thread: Powder burn rate VS Barrel length

  1. #1
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    Powder burn rate VS Barrel length

    A buddy figures that loading a faster powder in his .243 Win with a 20" barrel, will produce a greater muzzle velocity than can be achieved with a slower burning powder? I have always been under the impression that upwards of 97% of any powder was burned within a few inches of the chamber, which would make choosing a faster burn rate irrelevant. Also, his claim is that muzzle flash is caused powder that is still burning?
    Anyone have the facts?

  2. #2
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    In simple terms, he's right, but have a look at this current discussion & follow the links:

    http://benchrest.com/forums/showthread.php?t=68128

  3. #3
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    I have found the faster powders to usually be better in the shorter barrels. I have been using VV N-133 for several years in my 308 short barrels with 150 gr bullets.

    Better accuracy and less barrel heat.

  4. #4
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    QuickLOAD is an internal ballistics program that models what goes on after the primer lights the powder. It's a heck of a good teaching tool.

    I think the biggest advangage of fast poweder in short barrels is reduced muzzle exit pressure which may improve accuracy even though it reduces muzzle velocity. To get the same MV out of a shorter barrel requires higher average pressure for a shorter time which isn't going to happen with a faster powder because all the powders are constrained by the same peak pressure limits.

    Fitch

  5. #5
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    There was an artical in PS about a million years ago on this very topic. They took a bunch of long bbls, found the powder with the highest FPS for each tube, then started cutting the bbl shorter and re tested. They found that with any spacific bbl, the powder that worked best in a long bbl worked best as it got shorter.

    Go figure. Anyone else remember.....I have a fantastic memory...it's just that it is only an inch long!!!!!

    Tod

  6. #6
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    Wink Tod is wrong

    Quote Originally Posted by Tod Soeby View Post
    There was an artical in PS about a million years ago on this very topic. They took a bunch of long bbls, found the powder with the highest FPS for each tube, then started cutting the bbl shorter and re tested. They found that with any spacific bbl, the powder that worked best in a long bbl worked best as it got shorter.

    Go figure. Anyone else remember.....I have a fantastic memory...it's just that it is only an inch long!!!!!

    Tod
    Tod there was no Precision Shooting magazine back then.They didn't even have type writers back then.We also know there were no lawyers back then because reports of men dragging women by their hair continue to be received.

  7. #7
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    Quote Originally Posted by Worker View Post
    Tod there was no Precision Shooting magazine back then.They didn't even have type writers back then.We also know there were no lawyers back then because reports of men dragging women by their hair continue to be received.
    You are right--it wasn't a million years ago. It was only in 1244 BC. I remember it well. But there was only one powder available for testing back then, H4831.

  8. #8
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    I read some of these articles also. But they were not published in 1244 BC. They were published in 2041 AD. :-)

    What struck me is how various calibers differ so much from one another as the barrel gets shortened.

    For some calibers, like the .308, there was minimal reduction in velocity as the barrel shortened.

    One caliber that got much affected -- for unknown reasons -- was the 270 Win. THis stuck in my memory because I own one.

    -----------

    I know this is almost heresy around here to question any fundamental assumptions, but - - wouldn't it make sense to get a longer barrel?

    Personally, I would not want a 20 inch rifle in one of the hotter calibers. It's almost like . . . making your own problems for yourself.

    I suppose I have offended someone out there ... if so, sorry in advance.

    Enjoy your shooting --

  9. #9
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    Quote Originally Posted by Montana Pete View Post
    I read some of these articles also. But they were not published in 1244 BC. They were published in 2041 AD. :-)

    What struck me is how various calibers differ so much from one another as the barrel gets shortened.

    For some calibers, like the .308, there was minimal reduction in velocity as the barrel shortened.

    One caliber that got much affected -- for unknown reasons -- was the 270 Win. THis stuck in my memory because I own one.

    -----------

    I know this is almost heresy around here to question any fundamental assumptions, but - - wouldn't it make sense to get a longer barrel?

    Personally, I would not want a 20 inch rifle in one of the hotter calibers. It's almost like . . . making your own problems for yourself.

    I suppose I have offended someone out there ... if so, sorry in advance.

    Enjoy your shooting --
    Wow, we have a time traveller!

    Regarding the difference between .308 and .270, it has been generally understood that the case capacity VS bore capacity as well as the ratio of bore diameter to length are responsible for this effect. Small powder capacity/large bore capacity (.308) is less affected by length than large powder capacity/small bore capacity (.270)

    I'm not sure how to interpret the heresy/assumption portion of the post but generally hunting rifles are first built around handling/balance and all else follows. Only for controlled situations like varmint hunting or stand hunting can the long barrel be used effectively. For carrying purposes real hunting rifles are made shorter.

    And ammunition mfgrs react accordingly, tailoring their offerings toward the common denominators in the available market. Handloaders can be more specific in addressing their personal setups.

    al

  10. #10
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    Alinwa wrote, I'm not sure how to interpret the heresy/assumption portion of the post but generally hunting rifles are first built around handling/balance and all else follows. Only for controlled situations like varmint hunting or stand hunting can the long barrel be used effectively. For carrying purposes real hunting rifles are made shorter.
    I respectfully disagree. It makes no sense to purchase a flat-shooting western rifle, then bob the barrel to the point that it is compromised in its original concept, and becoming something of a "blast cannon."

    If you want a short-barreled rifle, why not get a cartridge that's balanced and not overbore? In that case, forget the .270 win. Find something else.

    You write that "Only for stand hunting can a long barrel be used effectively." You might want to try that line out on the mule deer, elk, and antelope we took in Montana -- they might disagree with you. One of us used an old 24-in.-barreled classic, another used a 22-in. Rem 700. Not everyone hunting out West needs to walk all day with a rifle -- there are jeeps, you know. We certainly had one.

    I suppose this is some sort of blasphemy or something, but I have a great deal of trouble finding much sense in your postings . . . . . The more of them I read, the less simple common sense I find. Your current post seems pretty incomprehensible to me. Hope you enjoy your 20-inch barreled gem.

    Best--

  11. #11
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    Quote Originally Posted by Montana Pete View Post
    I respectfully disagree. It makes no sense to purchase a flat-shooting western rifle, then bob the barrel to the point that it is compromised in its original concept, and becoming something of a "blast cannon."

    If you want a short-barreled rifle, why not get a cartridge that's balanced and not overbore? In that case, forget the .270 win. Find something else.

    You write that "Only for stand hunting can a long barrel be used effectively." You might want to try that line out on the mule deer, elk, and antelope we took in Montana -- they might disagree with you. One of us used an old 24-in.-barreled classic, another used a 22-in. Rem 700. Not everyone hunting out West needs to walk all day with a rifle -- there are jeeps, you know. We certainly had one.

    I suppose this is some sort of blasphemy or something, but I have a great deal of trouble finding much sense in your postings . . . . . The more of them I read, the less simple common sense I find. Your current post seems pretty incomprehensible to me. Hope you enjoy your 20-inch barreled gem.

    Best--
    Hey! You've isolated something we can agree on......

    I have little or none of your "common sense," as you so kindly pointed out.....

    agreed, in spades



    al

  12. #12
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    Red face Totally insulted by Montana Pete

    Montana Pete on a scale of 1-10 just how sorry are you ? Rev Al Sharpton will be notified !!!!!

  13. #13
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    Exclamation Vicvanab is in the hot seat

    Quote Originally Posted by vicvanb View Post
    You are right--it wasn't a million years ago. It was only in 1244 BC. I remember it well. But there was only one powder available for testing back then, H4831.
    For the record it was Marco Polo that traveled to China and discovered IMR 3031......... Another thing when the Oakland Raiders played the Patriots in the snow it was a fumble !!!!!!!!!!!

  14. #14
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    "I have always been under the impression that upwards of 97% of any powder was burned within a few inches of the chamber, which would make choosing a faster burn rate irrelevant."

    You are correct, so far as velocity is concerned. And I assume that's what you're referring to.

  15. #15
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    Slow burn powders such as 4831 in short barrels, 20" with big cases such a the 3006 will burn powder past the end of the barrel. If you shoot late evening you can see the flash. You can see the difference between the faster and slower powders.

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