New AR. 18" or 20" barrel?

[a1fabweld]

Hey all. I'm in the market for another upper & I thought I'd build one from scratch. I want to focus this one on longer range target shooting than my current 16"ers. I was looking at WOA's 18" SPR barrel w/rifle gas system or their 20" SDM barrel. Is there much advantage from the 20" over the 18"? Either will get scoped & I'll be shooting 55 to 77 grain bullets. Thanks for your thoughts.

[GenLee]

16" Dissipator my friend. Best of both worlds.

[OutlawDon]

I'm in the same exact boat currently. I just sold my WOA 16" barrel to a forum member and was looking at an 18" or 20" barrel as a replacement for a little more velocity and energy. I am not busting down doors so I realized I don't need a short carbine length type AR. Barrels are just hard to find these days with low stock everywhere so beggers can't be chosers. I ended up getting a 20" stainless match barrel from Armalite few days ago as they were the only company that had a longer stainless barrel in stock anywhere without a wait. Jump on it if I were you....

http://www.armalite.com/ItemForm.aspx?item=B15A2S&Category=a5c527d6-017c-40c2-80f2-59e99534f863

And if you look at my posting below of velocity as a function of barrel length, you'll see that the gain from 18" to 20" is minimal, but the gain from 16" to 18" is much more. I would have gone with a 18" barrel but no one has them in stock, so the 20" is fine. The tiny gain can't hurt either.

http://www.calguns.net/calgunforum/showthread.php?t=157460

MK 262 (77 grain) 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 (62 Grain) 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 (55 Grain) 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

[Linus]

...velocity as a function of barrel length, you'll see that the gain from 18" to 20" is minimal, but the gain from 16" to 18" is much more. I would have gone with a 18" barrel but no one has them in stock, so the 20" is fine. The tiny gain can't hurt either.

That was my logic when I got my CMMG 18''Stainless SPR barreled upper, I wanted something slightly lighter and more compact than a 20" upper without sacrificing performance and accuracy. So go for the 18" barrel if you can find it if not go for the 20" upper and shoot the hell out of it, IMO.