Hey guys, I need some advice.  I am looking a the 20'' A1 barrel that green Mountain makes.  I have a couple of their barrels and am a fan for sure.  They are good people to boot.  

Here is what I would like:  I'm not an A1 guy, or even a retro guy.  But...the 20'' lightweight is appealing.  I would like to build an upper, and use a FF tube on it, like the ALG in a 15'', for a lighter gun with a longer sight radius, for some 3 gun type shooting, and carbine classes.  My main concern, is the 1/12'' barrel.  

I realize they are old school gangsters, and mainly for 55 gr. M193 type ammo, but what is their limit?  Would they stabilize  M855?  Or is a 62 just usually too much?  

Thanks for the input guys.

I've heard reports of keyholing with M855, never tried it though.


What little I know about the 1/12, it's great for 55 grain, not much else.

There's always the McKay barrels, they are 1/7.

http://www.mckay-ent.com/parts/m16-a1-replacement-barrel.html

Del-Ton has 20" light weight 1/9 barrels.  The gas block section is 0.750" OD.

http://www.del-ton.com/Del_Ton_Inc_Barrels_p/bl1028.htm

I would expect keyholing from a 1:12" bbl @ 100 yds w/ M855.  The Army does.  Think the Swiss use a 1:9.5 for their 62 grn bullets.  That's about the minimum.  1:7" is the minimum for M856, b/c it's longer than M855.

I used an alpha shooting sports barrel for my A1 build.  Great accuracy with 55 gr bullets.  Haven't tried anything else yet.

I have a green mountain pencil barrel in my m16a1 build with a 1:12 twist. As others have mentioned and from my own tests, yes m855 starts to keyhole around 80-100 yds out. Worst case scenario if you really want to shoot the longer ss109 bullets you could have adco recountour a 20" barrel with a 1:9 or faster to a pencil A1 profile.

No need to reprofile:

http://www.mckay-ent.com/ar15-m16/m16-a1-replacement-barrel.html  

http://www.fulton-armory.com/barrelfa16m4gicontourcm1x9threadedchromelined-1.aspx  

http://shop.ar15sport.ihoststores.com/productinfo_v3.aspx?productid=BARREL-20LWT19