Author Topic: 7.62x39 velocity  (Read 1682 times)

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VJBUM

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7.62x39 velocity
« on: July 29, 2009, 08:50:46 PM »
I was reading about the Tabuk 7.62x39 DMR being used in Iraq and wondered how much bullet velocity  increased in the 22.5" barrel SKS over a 16.5" barrel rifle. Ballistic info for the 7.62x39 is almost always for a 16" barrel (AK) rifle. How much difference does the extra 6" of barrel length make?
« Last Edit: July 29, 2009, 08:58:04 PM by VJBUM »

gunlover

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Re: 7.62x39 velocity
« Reply #1 on: July 29, 2009, 09:16:11 PM »
A longer barrel produces a higher rate of spin which stabilizes the round for accuracy... As to the figure I would guess that it may increase velocity of about 4-5% maybe slightly higher...

Some other member that hand loads will come around and probably give you a better figure....  GL
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murray

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Re: 7.62x39 velocity
« Reply #2 on: July 29, 2009, 10:52:01 PM »
IIRC, it's 25 to 50 fps faster per inch of barrel length. (YMMV) 150 to 300 fps faster isn't much.

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hardcase

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Re: 7.62x39 velocity
« Reply #3 on: July 30, 2009, 09:51:37 AM »
Also, once the powder is completely burned, additional barrel length will ever so slightly decrease velocity.  This topic comes up all the time over at rimcentral.com.  It's usually good for a page or two of interesting information, then a few more pages of name calling  :lol:

I agree with both Murray and Gunlover.  There's not much extra velocity.


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smoke63b

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Re: 7.62x39 velocity
« Reply #4 on: July 30, 2009, 10:56:58 AM »
If any extra...

I think they always use 16" for a lot of velocity numbers because that's a good cutoff for max velocity. Depending on the round it will have a maximum barrel length that's effective and then after that it actually gets slower.

martin08

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Re: 7.62x39 velocity
« Reply #5 on: July 30, 2009, 12:22:03 PM »
Can't find the thread right now...

I read here once about chronographing a Paratrooper (16") and standard (20.5") and finding only 15 -20 fps difference.

It seems that the gas port length is roughly the same on both guns and the projectile gets it's maximum pressure only to the point of the gas port.

I may be all wet.... but I seem to remember reading it here?

nhblaze

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Re: 7.62x39 velocity
« Reply #6 on: July 30, 2009, 12:35:47 PM »


It seems that the gas port length is roughly the same on both guns and the projectile gets it's maximum pressure only to the point of the gas port.


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Martin08   I do believe that is the CORRECT answer !!

Most reloading manuals that I've seen use a 22" barrel for the velocities that they quote, like from a bolt gun.
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LS6TT

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Re: 7.62x39 velocity
« Reply #7 on: July 30, 2009, 12:43:45 PM »
A longer barrel produces a higher rate of spin which stabilizes the round for accuracy...

I think that isnt 100% accurate.  If you take a barrel and cut it down to a shorter length then created then agree.  but if the barrel is made in that length the accuracy isnt effected. now the distance is.

VJBUM

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Re: 7.62x39 velocity
« Reply #8 on: July 30, 2009, 03:05:54 PM »
Thank you all for the replies. Research using European ammo has shown an increase in velocity from 2330fps to 2475fps in a 22" barrel over a 16" barrel. Murray, you got it right,thanks. I know that the powder charge, in a x39, does not burn completely, because the muzzle flash is caused by unburned power igniting when it contacts the oxygen in the air,causing it to ignite. Its the quality of the ammo that counts. Surplus ammo can show that much difference round to round from the same box.

nhblaze

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Re: 7.62x39 velocity
« Reply #9 on: July 30, 2009, 03:18:57 PM »
Its the quality of the ammo that counts. Surplus ammo can show that much difference round to round from the same box.

+1   :thumbright:
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phargolf

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Re: 7.62x39 velocity
« Reply #10 on: July 30, 2009, 08:20:22 PM »
+2