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iRidiculous
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Posted: 12/13/2011 12:28:01 PM
I can't decide if I want a 20 in barrel or an 18 inch. Currently I'm looking at the LaRue Stealth Uppers and am wondering if there's a functional difference besides the weight. What does the extra two inches give me?
Saddlerocker
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Posted: 12/13/2011 12:32:14 PM
[Last Edit: 12/13/2011 12:32:28 PM by Saddlerocker]
Velocity would be the difference.
The 18" would technically be more rigid and theoretically more accurate given the same barrel profile.

EdgecrusherXES_45
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Posted: 12/13/2011 12:33:01 PM
I think 18" is that sweet spot for AR rifles.

Difference you will not see much if any between the two other than one is two inches shorter.
If something seems to good to be true it is best to shoot it just in case! - Fiona Glenanne
iRidiculous
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Posted: 12/13/2011 12:37:54 PM
What is the velocity difference between the 18 and 20 inch barrels? Is there a big difference in the optimal range for each length?
Winn
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Posted: 12/13/2011 12:59:15 PM
Originally Posted By iRidiculous:

What is the velocity difference between the 18 and 20 inch barrels? Is there a big difference in the optimal range for each length?


Depends on the ammo, but not much.

As mentioned above, in general, 5.56 ammo is basically "maximized" out of barrels that are approx. 18.5" long.

18.0, 15.50, 13.0 ...

Poznai Sebia - Know Yourself.
pistolpete
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Posted: 12/13/2011 1:06:38 PM
[Last Edit: 12/13/2011 1:19:45 PM by pistolpete]
I grabbed this from a thread posted by Geohans. Not sure how accurate it is.

EDIT, link to thread added:
http://www.ar15.com/forums/t_3_12/450544_Velocity_Barrel_Length.html




MK 262 VELOCITY DATA
__________________________________


7.5" 2053 FPS ... 10.5" 2363 FPS
DIFFERENCE 310 FPS
DIFFERENCE/INCH 103 FPS

10.5" 2363 FPS ... 14.5" 2576 FPS
DIFFERENCE 213 FPS
DIFFERENCE/INCH 53 FPS

14.5" 2576 FPS ... 16" 2669 FPS
DIFFERENCE 93 FPS
DIFFERENCE/INCH 62 FPS

16" 2669 FPS ... 18" 2769 FPS
DIFFERENCE 100 FPS
DIFFERENCE/INCH 50 FPS

18" 2769 FPS ... 20" 2818 FPS
DIFFERENCE 49 FPS
DIFFERENCE/INCH 25 FPS



M855 VELOCITY DATA
__________________________

7.5" 2244 FPS ... 10.5" 2639 FPS
DIFFERENCE 395 FPS
DIFFERENCE/INCH 132 FPS

10.5" 2639 FPS ... 14.5" 2861 FPS
DIFFERENCE 222 FPS
DIFFERENCE/INCH 56 FPS

14.5" 2861 FPS ... 16" 2938 FPS
DIFFERENCE 77 FPS
DIFFERENCE/INCH 51 FPS

16" 2938 FPS ... 18" 3046 FPS
DIFFERENCE 108 FPS
DIFFERENCE/INCH 54 FPS

18" 3046 FPS ... 20" 3061 FPS
DIFFERENCE 15 FPS
DIFFERENCE/INCH 7.5 FPS


XM193 VELOCITY DATA
_________________________________


7.5" 2364 FPS ... 10.5" 2755 FPS
DIFFERENCE 391 FPS
DIFFERENCE/INCH 130 FPS PER INCH

10.5" 2755 FPS ... 14.5" 2984 FPS
DIFFERENCE 229 FPS
DIFFERENCE/INCH 57 FPS PER INCH

14.5" 2984 FPS ... 16" 3075 FPS
DIFFERENCE 91 FPS
DIFFERENCE/INCH 61 FPS

16" 3075 FPS ... 18" 3245 FPS
DIFFERENCE 170 FPS
DIFFERENCE/INCH 85 FPS

18" 3245 ... 20" 3254 FPS
DIFFERENCE 9 FPS
DIFFERENCE/INCH 4.5 FPS
Winn
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Posted: 12/13/2011 1:16:57 PM
[Last Edit: 12/16/2011 8:27:08 PM by Winn]
Originally Posted By pistolpete:

I grabbed this from a thread posted by Geohans. Not sure how accurate it is...


Those numbers were originally posted by MSTN. It's a safe bet that they're very accurate.

Glad you posted them too. They used to be in a tacked thread that MSTN had here, but has long since disappeared.

18.0, 15.50, 13.0 ...

Poznai Sebia - Know Yourself.
iRidiculous
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Posted: 12/13/2011 4:13:16 PM
Awesome, thank you!