AR-10 .308 Accuracy vs Barrel Length

[Safetychain]

My son is looking to build an AR-10 .308 on a PSA lower and concerned that the available barrels from PSA are only 16 & 18 inches. Is it really necessary to have a 20" or plus length barrel to get an accurate hunting rifle? I have always had the impression that burn time of the powder could be selected to match the barrel length to get the speed desired and the barrel length really didn't have that significant effect on the accuracy except when going for super sniper rifle type accuracy at really extended ranges. He's working to get a longer range type deer hunting rifle than what he has access to, a .30-.30 lever and an AR-15 in .223 and wants to keep with the AR type platform. He already has the PSA AR-10 lower. Of course it would be wonderful if some commercial brand of ammo would shoot great but I've always found that reloading my own and tuning the ammo to the rifle in hand always resulted in the best accuracy. I've done this for many rifles, including .308, in the past and will work with him on this whatever barrel length he goes with.

 

[strambo]

If anything, a shorter barrel is more accurate due to it being more rigid. Length just affects velocity. The 18" should be just fine and get decent velocity. 16" 7.62 ARs have been shot out to 800+ no problem.

 

[ironworkerwill]

Short ridged accurate+1

Not saying long barrels can't be accurate but they not as loud

Light for caliber bullets using a faster for caliber powder works good for my long barreled rifles too!

 

[LUCKYDAWG13]

i had a 17" 308 Encore barrel not a AR10 i know but shot real good

 

[LocoGringo]

I have a highly modified DPMS LR-308 with an 18.5" barrel that has excellent accuracy (sub-MOA, 5-shot groups regularly). For hunting I use the Hornady 178 Amax (heavy for .308) handloaded and get a muzzle velocity of 2560 FPS without pushing pressures to the limit. That is plenty to get out to ethical hunting distances. It will depend a lot on what trigger he decides to use and mostly on the barrel. Those are not places to go cheap. To further tune things, I would recommend an adjustable gas block from SLR Rifleworks or Syrac Ordnance (Gen II). Just be careful about weight because it is easy to build a fat pig of a rifle that can weigh over 10 pounds.

 

[Vern Humphrey]

Is it really necessary to have a 20" or plus length barrel to get an accurate hunting rifle? I have

Barrel length has nothing to do with accuracy. It only affects velocity (and hence kinetic energy.)

 

[dvdcrr]

For point of reference my mp10 18" lightweight tube does very consistent 2" three or four shot groups at 220 yds with ammo it likes and 3" groups at 220 yds with run of the mill.

 

[B!ngoFuelUSN]

Barrel length has nothing to do with accuracy. It only affects velocity (and hence kinetic energy.)

Well actually it does. Or does in theory. Whether a typical shooter will see a difference is an exercise left for the reader.
The principal is that the longer the barrel, the more amplitude in harmonic vibrations (and likely a different frequency as well). Short barrels vibrate less and thus are more accurate. But less speed and thus reduced range. Life is loaded with tradeoffs.
B

 

[Vern Humphrey]

Well actually it does. Or does in theory. Whether a typical shooter will see a difference is an exercise left for the reader.
The principal is that the longer the barrel, the more amplitude in harmonic vibrations (and likely a different frequency as well). Short barrels vibrate less and thus are more accurate. But less speed and thus reduced range. Life is loaded with tradeoffs.
B

Not quite. What affects accuracy is the synchronization of the load with the barrel harmonics. If bullets are exiting at the node, rather than between nodes, the rifle will be more accurate (that's the principle Browning used in its barrel tuner.)

This synchronization has nothing to do with the length of the barrel.

 

[back40]

being that a shorter bbl is stiffer, wouldn't that increase the instances of various ammos exiting at the nodes as opposed to between....therefor generally making them 'more accurate' in a sense? (tuners aside)

 

[Tirod]

Barrel length has everything to do with shooter self image. What's fun is to read all the prose as they jump thru hoops to justify it.

Here's just a few articles on the subject: http://www.thetruthaboutguns.com/20...-applications-short-barreled-precision-rifle/

http://www.backwoodshome.com/articles2/ayoob136.html

http://www.tacticaloperations.com/SWATbarrel/

Which are just the tip of the iceberg: https://www.google.com/search?q=bar...ceid=chrome&es_sm=93&ie=UTF-8#q=barrel+length

Can you go "too short?" Sure, just the same as too long, and when rifle and cartridge makers are attempting the highest possible velocity from a given combination, longer barrels give them better numbers to use in advertising.

This is where male ego enhancement starts to intrude on practicality. Like trying to use a target rifle deer hunting, the ugly reality is that a 2MOA is quite sufficiently effective as it shoots a ten inch hit zone at 500m, but the intended target is twice that just in the size of it's vitals. Both whitetails and humans have about an 18" center of mass zone of vitals.

Prairie dog hunting, sure, a .5MOA gun may not be good enough. Minute of prairie dog head is NOT the standard for every rifle you need to own, tho. It's quite expensive and renders it impractical for other uses.

It's why I find the current fad to buy 18" barrels for the 6.8SPC to be silly. The cartridge was designed to be used in a 14.5" and making it longer for some incrementally higher speeds is a target range application. It does nothing to improve it in a combat or hunting rifle accept make it harder to move quietly in deep cover where game animals lie up during the day.

As barrels get shorter, the composition of the cartridge can be modified to compensate. The Navy is using some 10.5" short barreled issued M4's on board ship, they went to a 77 gr bullet with a lot more flash suppressant in the powder.

You can, too. I'm building a legal version - the AR pistol - for my next hunting weapon. Most deer are usually shot within 125 yards, generally much shorter ranges in deep cover, and the shorter AR pistol as effective ballistics in that use. The added bonus is that I can use it in those seasons when rifles are not allowed, and I consider it a better choice than a 9mm with 3.5" barrel.

Frankly, the fly in the ointment is the 1934 NFA which arbitrarily dictates barrel lengths which a honest citizen is restricted from using without stamps or stocks. It's relatively meaningless now with the SIG wrist brace, but it shows the ingenuity of man in getting around ridiculous legislation.

 

[OpticsPlanet]

I've seen reports of people shooting their Larue OBR with a 16" barrel at 1000 yards no problem.

Tim G.

 

[ironworkerwill]

Read this, it may change your life. http://www.angelfire.com/ma3/max357/houston.html

Then look at this. http://www.bellmtcs.com/store/index.php?cid=580

Often, regardless of barrel length, an accurate load can be found.

 

[taliv]

Not quite. What affects accuracy is the synchronization of the load with the barrel harmonics. If bullets are exiting at the node, rather than between nodes, the rifle will be more accurate (that's the principle Browning used in its barrel tuner.)

This synchronization has nothing to do with the length of the barrel.

while your first paragraph is true, it is also a matter of amplitude. use extreme examples to illustrate of maybe a 5" barrel and a 30 foot barrel. the longer barrel will whip up and down further than the shorter barrel, so your timing has to be more precise.

Barrel length has everything to do with shooter self image. What's fun is to read all the prose as they jump thru hoops to justify it.

Here's just a few articles on the subject: http://www.thetruthaboutguns.com/201...ecision-rifle/

http://www.backwoodshome.com/articles2/ayoob136.html

http://www.tacticaloperations.com/SWATbarrel/

yeah. "the truth about guns" blog is probably the worst disinformation I've seen in a long time. it really chaps my cheeks when guys with little experience use atrocious logic to reach demonstrably false conclusions while continuously repeating "everybody disagrees with me but it's the truth". that article is a great example.

I've seen reports of people shooting their Larue OBR with a 16" barrel at 1000 yards no problem.

yep. as long as you don't need first round hits, your targets are modeled after People of Walmart, and you have the luxury of only shooting on calm, no-wind days, that's a great choice.

Read this, it may change your life. http://www.angelfire.com/ma3/max357/houston.html

oldie but goodie

 

[ironworkerwill]

your targets are modeled after People of Walmart

HEY, you can't misrepresent my people like that! I assume you meant larger than normal.

use extreme examples to illustrate of maybe a 5" barrel and a 30 foot barrel.

Absolutely!

 

[ssyoumans]

Go for a lightweight upper. Not very much fun toting around a 10 - 11 lb AR10. I have a Remington R25 with 20" partially fluted barrel. It is a lot heavier than my T/C Venture in 308 with a 22" barrel.

 

[Vern Humphrey]

being that a shorter bbl is stiffer, wouldn't that increase the instances of various ammos exiting at the nodes as opposed to between....therefor generally making them 'more accurate' in a sense? (tuners aside)

The dwell time of the bullet must be correct for the natural harmonics of the barrel, barrel length has nothing to do with that.

Now both dwell time and harmonics will be DIFFERENT for barrels of different lengths -- but if the bullet doesn't exit at a node, it will not be an accurate load, regardless of its length.

 

[Art Eatman]

My 19" .243 and my 26" .30-'06 have been sub-MOA regularly and reliably for over forty years.

FWIW.

 

[back40]

perhaps taliv said it better...

while your first paragraph is true, it is also a matter of amplitude. use extreme examples to illustrate of maybe a 5" barrel and a 30 foot barrel. the longer barrel will whip up and down further than the shorter barrel, so your timing has to be more precise.

the longer bbl has less room for error with regard to dwell time, therefor making the shorter bbl generally more accurate (in a practical sense) with more loads.

 

[Unlicensed Dremel]

Is it really necessary to have a 20" or plus length barrel to get an accurate hunting rifle?

Short answer: No

Long answer. No. Definitely the answer is no. Not only is it not "really necessary; it's not necessary at all. Barrel length has nothing to do with intrinsic accuracy past about 7", I believe...maybe less. If anything, longer bbls can sometimes detract from accuracy, but this *usually* only happens past about 27 or 28".

However, the longer barrel will cut down some on muzzle blast, which could reduce flinch. This is the best reason for a longer barrel. And perhaps for more dwell time, for better gas system functioning.

And the longer bbl could lead to better *practical* accuracy (not actual accuracy) in the wind, at longer ranges (past 200 yards, which is extremely uncommon for hunting).

 

[Vern Humphrey]

There are three reasons for a long barrel:

1. To obtain maximum velocity.

2. To obtain maximum sight radius when using iron sights.

3. To move the muzzle blast farther from you ears.

 

[HKGuns]

16.5" 762 AR @100 yards with hand loads.



Same 16.5" 762 AR @200 yards with hand loads.

 

[Welding Rod]

Nice, What is the handload?

 

[Lycidas Janwor]

FWIW I've been told that an 18" barrel for an AR10 platform rifle is pretty much the max length you want and to get anything over that is unecessary.

 

[Khromo]

I believe the quality of the barrel has a much greater impact on the accuracy of the finished rifle than the barrel length, within reasonable limits.

If I were assembling an AR-10 pattern rifle (I've never assembled one, but I understand it is not cheap!) I would not economize on the barrel, no matter how much longer it took to get it finished.

Get a great barrel. Don't let a discount vendor's selection influence your choice. Get a great barrel, 18 to 22 inches, and you will never regret the cost.