.308 IN barrel burn rate...
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Old 09-13-2011, 02:23 AM   #1
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Default .308 IN barrel burn rate...

I was just watching a youtube video about a specific rifle with a 16 inch barrel. It was chambered for .308. The narrator states " the .308 cartridge needs at least 18 inches of barrel length to fully burn all the powder in the round." Is this a true statement, if so, of what kind of powder..? are there not quicker burning powders for re-loaders ( aside from the obvious pistol, shotgun, rifle, and black powder groups) ? During my life, as a child, I was very proficient in the area of re-loading .357 ammo for my dad. Since then I have done very little re-loading, but just had to ask, I'm afraid I have become spoiled in just having "Uncle Sam" supply it. I'm retired now and will be making a quick turn to doing it for myself as seeing the current cost, and quality variances in the ammo sold over the counter. Any help would be appreciated.
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Old 09-13-2011, 04:02 AM   #2
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18" is not enough either. If it was, an M-1A would not need a flash hider
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Old 09-13-2011, 04:18 AM   #3
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There is a reason that most center-fire rifles have 24" barrels.
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Old 09-13-2011, 04:42 PM   #4
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Quote:
Originally Posted by robocop10mm View Post
18" is not enough either. If it was, an M-1A would not need a flash hider
Aahh... That I remember !!! Common sense strikes again..!
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Old 09-13-2011, 06:55 PM   #5
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Shorter barrels require faster burning powder. Easy to do when reloading but factory loads are set for longer barrels.
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Old 09-14-2011, 01:42 AM   #6
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Even if all the powder was burned, it would still take significantly longer for the pressure behind the bullet to drop below the friction of the bullet. Basically, the bullet will probably continue to accelerate well beyond 30" of barrel length. Hell, most factory pistol rounds with their fast powders still don't start slowign down until 16-18" of barrel length, though the actual burning is probably done by 8-10".
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Old 09-14-2011, 04:45 AM   #7
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a .22 lr takes a 16" barrel to get max velocity. If I remember correctly.
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Old 09-14-2011, 08:47 PM   #8
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I remembered I had these pictures:


If a .308 has a similar pressure curve, and there is still 10k PSI at ~18" of barrel length, that's still over 700lbs of force pushing the bullet down the barrel, and 10k PSI to be released if the barrel ends there.
223barrelvelocities_pressure.gif   308barrelvelocities.gif  

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Old 09-14-2011, 11:41 PM   #9
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Excellent guys..! This is GREAT info..! So with this being said, even if I was to use a faster burning powder while re-loading my own ammunition, I would still never rech max muzzle velocity until around 25 to 30 inches of barrel length. Thank you all..!
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Old 09-15-2011, 12:45 PM   #10
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For years i owned a .308 with an 18" barrel. The muzzle blast was awful. Early one morning i shot a deer in low light and the muzzle flash blinded me for a minute or so. Traded that gun off and was not sorry to see it go.
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