Have a spare AR-10B upper/lower what would be most accurate for 300+ yards in 308 or creedmore ? 18" or 20"

Any Brands for a Armalite better than others ?

Thanks John

I was shooting 24" 308 Savage bolt and it was 1/2 MOA with good ammo, I would go as long as you can!

Longer barrels usually give greater velocities for a particular load.
They are not necessarily more precise (accurate). Many shooters who strive for maximum precision and don’t have other considerations such as flatter trajectories or the other advantages of higher velocities chose shorter, stiffer barrels.

For the purpose you mention, however, my personal choice would be the longer barrel length. In fact, I consider 20 inches to be a short barrel for either 308 Winchester or 6.5 Creedmoor. My most-used 308 bolt action has a 20" barrel, but it was acquired and set up for short distance shooting and the handiness and portability of a rifle with a short barrel was also important. My 308 TRG-22 is strictly a range gun and has a 26 inch barrel. My current 6.5 rifle has a 24" barrel, and I consider that to be a good balance between handiness and bullet velocity.

The flatter trajectories of higher velocities may not be a big deal at 300 yards, but higher velocities are an advantage when shooting in windy conditions.

Out to 300 yards, the accuracy differences between a 18" and 20" barrel are insignificant. At longer distances, longer barrels provide increased muzzle velocity, which will be noticed in bullet drop and drift.

The inherent accuracy of 308 Win and 6.5 Creedmoor cartridges are pretty similar. However, the 6.5 Creedmoor's recoil is noticeably less, and thus you will find it more accurate in normal use. 6.5CM bullets fly flatter and with noticeably less wind drift than 308, which will also increase your field accuracy. 308 generally has an energy on target advantage out to 400 yards -- 6.5CM carries more energy further out.

Due to the 6.5CM's smaller bore, its muzzle velocity benefits more from a longer barrel.

The downside to 6.5CM is barrel reduced barrel life. If you shoot with enough volume to wear out barrels, expect a 6.5CM barrel to have about 40% less life than a 308 Win barrel.

Understand that it is challenging for anyone to shoot a semi auto 308/6.5 with great precision. The platform isn't like a 223 AR15. The AR10 has more recoil, there's a huge hunk of BCG metal moving back and forth, and a lot of gas moving back down the gas tube. You'll find that with the 6.5CM's lower recoil, the fundamentals of marksmanship are easier to manage.

I have a DPMS-SR25 pattern AR10, which means I use Pmag magazines. I believe your AR-10B is a different pattern -- a different magazine and something different with the barrel. I don't know if my sources work for your 10B -- but you may ask at Fulton Armory, Compass Lake Engineering, and Craddock Precision.

My Armalite AR-10B -T has a 20 inch barrel; it's the one from the factory. It do not like that barrel as I think it's too thin and I have been considering getting a Krieger 20 inch with a muzzle diameter of 0.900 instead of the current 0.750.

About 12 years ago, I sent Krieger an Armalite AR-15 upper with the original 20 inch barrel and asked them to install a 26-inch barrel with the muzzle diameter of 0.900. They sent it back filly assembled and ready to go. It is a phenomenal rifle and I used it to good effect in F-TR competition for a few years.

As I said, I'm considering doing the same thing with my AR-10B. I would select a Krieger 20 inch @ 1:10 twist and the muzzle diameter at 0.900. It would be chambered in .308 Winchester as I am way too old to start another chambering and for 300 yards, it's not a big difference. I know the .308 very well.

I would also get the barrel bead blasted as this increase the surface area and the barrel cools faster.
Kriger offers the barrel for $435, the chambering and fitting for $275 and the bead blasting for $45. So about $700 and they ship you back an upper ready to go. They will headspace with your bolt.

https://www.kriegerbarrels.com/contours#ar10


The one thing that is stopping me is exactly what Fritz mentioned. The AR-10 is definitely NOT an AR-15. The 15 is a pussycat compared to the 10. I could actually run an entire F-class string (22 rounds) on my 15m while never even breaking cheekweld. My 15 has a through the triggerguard bolt release and I use a Bobsled to single load. I could get in position, on target, and shoot the string, without moving. The only thing my shooting hand would do is fish out the next round from the box and stuff in in the ejection port. The push the bolt release in the trigger guard and press the trigger. Rinse, repeat.

I have the ejection cycle tuned to where the brass piles up in a neat pile about 3 feet away from me at 4 o'clock. Or I would just leave my hard rifle case open next to me and all the brass would collect in there. There was virtually no recoil with that setup, just feed, push, press, repeat.

The 10 is quite different. That BCG is, in a word, substantial. The .308 has a lot more recoil than the 5.56, eve compared to my long range loads in .223. The 10 kicks, jumps and jars my jaw and head. And everything moves in there.

Don't get me wrong, it's a fun rifle to shoot and it can be very precise. but it requires a lot more, let's say, respect, than the 5.56/.223.

Perhaps with a heavier barrel it will be less bouncy, but I doubt it. I've tried a few competitions with it and I will continue to do that, but it's nowhere as easy as with the 15.

Speaking of magazines, the AR-10B has been discontinued for at least 3-4 years now and it takes its own magazine which is a modified M-14 mag. I bought a bunch of mags from Armalite when I got the rifle and a few years back, Brownells had them in stock and I bought more, knowing the AR-10B was discontinued. These mags are steel and built to last.

Here is a link to Brownells about these magazines.
https://www.brownells.com/maga...zines-prod31788.aspx

I would click on the Alert me when available button and hope for the best if you need more magazines.

I also found some at Cheaper Than Dirt.

I find these steel magazines to be quite superior to the plastic Magpuls I have for my AR-15s These steel mags are built like tanks.

I forgot to say that the reason I'm considering a 20 inch barrel is because of the rules of the game I am playing in. If there was no such rule, I would get a 24 inch, maybe even a 26 inch barrel.

I have three AR10's ~ 16,18.20.
They all have the same barrel mfg (Rainer Arms Shilen Ultra Match).
I would rate the accuracy (by comparison) >
16 > 85%
18 > 97%
20 > 100% (best)

The triggers are all the same Geissele but different optics that could account for some of the diference.

So seems the longer the better for me at least.

Thanks guys..

Looks like a 20" 0.90" Krieger Stainless bead-blasted, threaded and fit to the receiver/bolt with a gasblock will be just the ticket.


website for krieger was great

Good choice. Twist rate?

I'm looking forward to a range report on that setup.

On Twist rate

I have not made a call yet on 308 vs 6.5cm (leaning 6.5)

Is there an idea twist rate for ether in that barrel length ?

If I wasn't so invested in .308, I would go 6.5 CM. In a .308, I would suggest 1:10, regardless of barrel length.