PDA

View Full Version : Optimum Barrel length for AR 308 Platforms


evollep3
10-08-2009, 4:09 PM
I need your opinions I planning a little ahead right now I'm thinking of building another AR10 platform build but i cant descide on the barrel length 18", 20 or 24" again

I have a 24" Stainless now and to me its too front heavy from me but what is the "OPTIMUM" barrel length for 308? like 5.56 everyone always love the 18" but is the output the same for 308?

skkeeter
10-08-2009, 4:18 PM
Right smack down the middle. 20" gets my vote. It all really depends on how far you want to shoot with it. Longer the barrel, faster the speed of the bullet.

evollep3
10-08-2009, 4:33 PM
aha what if i throw a curve ball and say there is a 16" as well than there is no middle! :) 20" was what i was thinking if i get this 18" tomorrow if i trade my 24" but does the extra 2" make any significant difference cause the 5.56 didnt make that big of a difference

evollep3
10-08-2009, 4:37 PM
wheres Frank and Randall with their Hub Bub numbers! :)

tiger222
10-08-2009, 4:40 PM
16" on a 308 is no fun unless you are running a pig.
18.5" gets my vote, or 20"- 21" purely for comfort and balance.

bomb_on_bus
10-08-2009, 4:53 PM
20 inch is all I have, but I have seen some go as long as 26"

Currently I run a 20inch with a 1:10 twist.

I wouldn't feel comfortable running less than 20inches in .308 on a semi auto platform for what I use it for anyways. Although I have seen em as short as one foot.

Depends really on the type of barrel, twist rate, weight of bullet being shot etc.

Longer barrel means a faster muzzle velocity upon exiting the barrel, aslo allows for more bullet rotation in the barrel as opposed to shorter barrel lengths.

skkeeter
10-08-2009, 5:11 PM
aha what if i throw a curve ball and say there is a 16" as well than there is no middle! :) 20" was what i was thinking if i get this 18" tomorrow if i trade my 24" but does the extra 2" make any significant difference cause the 5.56 didnt make that big of a difference

You should gain around 100FPS with the extra 2". Don't hold me to 100 exactly as the pro's will eventually chime in. My younger brother who was trained as a Navy sniper had his rifle barrel cut to 20" and easily makes 1000y shots with it.

Fjold
10-08-2009, 5:37 PM
It depends on what you are going to use it for. Chuck Hawk has a good write up on barrel lengths and the effects of changing it here: http://www.chuckhawks.com/rifle_barrel.htm

Generally in a lower expansion ratio cartridge like a 308 you will see a change in velocity of about 30-40 fps per inch of barrel length but individual barrels of the same length could have that much (or more) variations. One barrel of 20" may shoot at 2700 fps and an identical barrel made by the same manufacturer may shoot the same load to 2800fps. But again generally that's why people buy premium barrels from reputable barrel makers because they will be much more uniform in dimension and finish with less variation between barrels.

If you use a program like JBM you can input different velocities for the same bullet and see their downrange ballistics. Try it out and see what barrel length (velocity) will work the best for your application.
http://www.jbmballistics.com/~jbm/cgi-bin/jbmtraj-5.0.cgi

I'm a longer barrel person myself. For a 308 used for long range work I want all the barrel that I can comfortably carry for the discipline I'm shooting. In a combination use gun (varminter/target) I like 26" in a #5 contour or so as a good compromise between length and weight. For a semi-auto used for general target shooting out to 600 yards or so my minimum would be 22" and if the choice is between 20" and 24", it would be 24" every time. You can always shorten a good barrel if you don't like it but you can't lengthen it. You can change the balance of the rifle with a lighter contoured barrel if the gun is to muzzle heavy. Alternatively you can add butt weights but then your overall weight goes up.

Quick load can compute the optimum burn rate (max efficiency) for the 308 if you know what bullet weight and powder you use and for a common load with the 155 grain bullet and 46 grains of Varget powder, you will need more than 26" of barrel length to completely burn the charge before the bullet leaves the barrel.

Choosing a barrel length is not a science, it's a personal thing on how you feel handling the gun and what you use the gun for.

Sheepdog1968
10-08-2009, 5:40 PM
SAWT mag Dec 2000 (online article) used SD swat on bolt action and found same accuracy out of 26" and 18" barrel. My guess is that this likely same in semi auto all other things being equal.

technique
10-08-2009, 6:00 PM
There is a difference between making shots at 1000, making accurate shots at 1000, and having enough velocity to kill effectively at 1000.

What do you wanna do? I like 21in. - 22in.

evollep3
10-08-2009, 6:03 PM
well i figure my 18" will be my lighter weight 308 and maybe do some 600+ but daymn this 24" is heavy thats why i want to go as short as possible and as long as possible i hope that makes sense you know im just going to get the GAP upper or should i get the titan upper hmmmm.. maybe even the POF i dunno .......................

technique
10-08-2009, 6:09 PM
18-20in should be fine at 600 yards...

Fjold
10-08-2009, 6:13 PM
SAWT mag Dec 2000 (online article) used SD swat on bolt action and found same accuracy out of 26" and 18" barrel. My guess is that this likely same in semi auto all other things being equal.

Accuracy of a barrel is more a function of the quality of the barrel not the length. Dimensional uniformity and finish of the barrel is what makes the difference.

evollep3
10-08-2009, 6:17 PM
Accuracy of a barrel is more a function of the quality of the barrel not the length. Dimensional uniformity and finish of the barrel is what makes the difference.

heres one for you from the 3 choices GAP, Fulton or POF ?

technique
10-08-2009, 6:23 PM
Fulton still using Krieger?

J_Rock
10-08-2009, 6:47 PM
heres one for you from the 3 choices GAP, Fulton or POF ?

POF :laugh:

Id worry more about the jack hammer action of their piston system messing up accuracy than the quality of their barrel.

evollep3
10-08-2009, 6:48 PM
Barrel, Titan Rifle, 20" Medium Weight Stainless Steel, 1x12 Twist, Fulton Armory
NOTE: This Barrel Accepts .875" Gas Blocks.

Legendary Fulton Armory Accuracy and Quality
Medium Weight Contour for Reduced Weight
Uses Rifle Length Gas Tube Design for Reliability, Accuracy & Durability
.875" Gas Block Diameter
5/8"x24 Threaded Muzzle
1x12 Twist, 4 Grooves, Button Rifled and Lapped
Includes Barrel Extension
Criterion by Krieger
Chambered for .308 Win AND 7.62X51 NATO

evollep3
10-08-2009, 6:56 PM
POF :laugh:

Id worry more about the jack hammer action of their piston system messing up accuracy than the quality of their barrel.

You know i love my POF i have now and so far im GTG of any problems

Jpach
10-08-2009, 7:37 PM
OP, if you are considering GAP, DO IT! There is no reason not to if you are willing to drop the necessary $$$. Go look at the other thread (as I look to post the pic here) on .308 ARs and you will see the stupidly accurate group from a calgunners GAP .308 AR. Its also a 20" barrel I believe. Absolutely beautiful. Im going to get one some day.

Either way go the DPMS route, they use SR-25 mags and therefore will be able to use the soon to come PMAGs

EDIT-Here is the group of the GAP AR-10
I didn't know Noveske didn't offer their lower anymore..... here is the best group I've done... but must have been kinda lucky, cause I haven't done anymore that tight... though at ASR it easily hits steal out to 400yrds.
http://i16.photobucket.com/albums/b22/Kiwa25/Gun/PA070002.jpg

jmf_tracy
10-08-2009, 7:44 PM
here's your ticket:
fulton armory lower + GAP DPMS style upper 22" bartlein barrel 11:1 twist add the thruster brake if you can spare $$$

Ghillie-man
10-08-2009, 7:58 PM
24 inch SS

Jpach
10-08-2009, 8:03 PM
here's your ticket:
fulton armory lower + GAP DPMS style upper 22" bartlein barrel 11:1 twist add the thruster brake if you can spare $$$

HELL YEA. Or wait for the Iron Ridge Arms sidecharging upper. Thats what Im doing. I know that they have a FAL type side charger in testing (Like LWRC SABR) and the reciprocating sidecharger on the BCG type being tested, last I checked they were just unsure of which one they were going with. Im really hoping its the left side FAL side charging style.

tankerman
10-08-2009, 8:18 PM
There is a difference between making shots at 1000, making accurate shots at 1000, and having enough velocity to kill effectively at 1000.
If the goal is to have enough velocity to kill at 1000 yards, then why not just pick a cartridge designed for, or better at that purpose?

technique
10-08-2009, 8:30 PM
If the goal is to have enough velocity to kill at 1000 yards, then why not just pick a cartridge designed for, or better at that purpose?

I'll let Randall get technical...but, a 24in-26in barrel on a .308 will (or should) send a pill with enough velocity/energy to kill at that distance. More so than a .308 with say a 18in. barrel, there just may not be enough energy left to get the kind of results needed to fully put someones dick in the dirt.

bakokid
11-17-2009, 10:21 PM
20-22.....what exactly do u wanna do. just a battle rifle?sniper? also velocity is best when barrel is long enough to get complete powder burn, with this in mind u may achieve desired velocity with a shorter barrel buy testing powders(reloads) and different ammo. what ever u do starting with a 308 ar is a good way to go, one rifle if built right can make a good battle rifle while shooting with the accuracy of a bolt rifle.

C.G.
11-17-2009, 10:35 PM
There is a difference between making shots at 1000, making accurate shots at 1000, and having enough velocity to kill effectively at 1000.

What do you wanna do? I like 21in. - 22in.

The two barrels I will be ordering from Krieger will be 18" for shorter stuff and 22" for longer stuff.

Not that anybody trully cares but me, but my AR-10 forward assist BCGs arrived today.:cool2: That means I finally have the bolts to send to Krieger to have the barrels made.

C.G.
11-17-2009, 10:38 PM
If the goal is to have enough velocity to kill at 1000 yards, then why not just pick a cartridge designed for, or better at that purpose?

Because it is too easy with a .338LM?:D

m24armorer
11-17-2009, 10:40 PM
21 inch, 11 P5 Schneider.

JPB
11-18-2009, 6:28 AM
heres one for you from the 3 choices GAP, Fulton or POF ?

Out of these choices, I'd go GAP built on an Armalite receiver. Forged receivers beat extruded every time. Folks love to talk about magazines. Gen 2 mags from Armalite are about $30 each if you buy the 5 pack. The Gen 2 is a darn nice magazine (steel follower, steel body, park finished), bullet proof. For DPMS platforms you can choose from DPMS, C-Products, and KAC. Haven't heard too much good about the first two options, and I don't hazard to guess how much a KAC mag goes for. LaRue may be available soon (best hope), and Magpul has an unenviable reputation of presenting new products that never make it to production.

popeye4
11-18-2009, 6:34 AM
If the goal is to have enough velocity to kill at 1000 yards, then why not just pick a cartridge designed for, or better at that purpose?

To shoot accurately at 1000 yds, the bullet has to stay supersonic. I don't want to get hit by a 155 gr or 175 gr supersonic .308 bullet, I think it would ruin my day.

The M14 has (I believe) a 22" barrel (or close to it). Long range competition guns can have 28" or longer barrels plus extension tube to get the front sight out as far from the eye as possible. .308 is really reaching its limit at 1000 yds.

Are you going to be mainly shooting or carrying? If your 24" barrel is making the gun too muzzle-heavy, put a counterweight in the stock (if it has the fixed stock with a cleaning rod compartment). Sure, its heavy, but it will be a pleasure to shoot. But if you spend more time carrying the rifle, go with a shorter, lighter configuration. I'd stay away from 16" as I'll bet that has quite the muzzle blast.

Will you be handloading for this rifle? You might be able to tailor your loads somewhat for the barrel length.

JTROKS
11-18-2009, 6:37 AM
If I was to hunt with it a 20" medium barrel will do, but if my purpose was to shoot a 1000 yard tactical match in semi auto class then a 24" heavy bull will be it. When going for the longer barrels the powder you used will make a difference in how much FPS you'll be gaining. I know, I know, you can only stuff so much Varget in a 308 case for a stiff compressed load before the case starts to bulge.

Army GI
11-18-2009, 7:52 AM
Short barrels can shoot far, though with more bullet drop.

But if you want to be competitive with other long range rifle shooters, don't go with the short barrel. Not too many 600+ yard competition shooters use 16" or 18" barrels.

Solidsnake87
11-18-2009, 7:57 AM
Tell us more about what you want to use it for. If its just a plinker or hunting gun, 16-20" is fine. If you want to shoot to 1K year round 26"+ is the way to go. When I finish my AR-10 Palma rifle it will rock a 33" krieger.

WeekendWarrior
11-18-2009, 1:42 PM
WWRTW

Jicko
11-18-2009, 1:48 PM
heres one for you from the 3 choices GAP, Fulton or POF ?

GAP w/ Bartlein barrel

20"

That would be MY CHOICE.



Short barrels can shoot far, though with more bullet drop.

For say, 16"..... VERY DIFFICULT to get enough velocity to get to 1000yds.

phish
11-18-2009, 1:52 PM
I'd be careful trying to reach the higher velocities reported by those with short barreled .308s. Those are running tight bore barrels on a bolt action. You have to take into account the gas system on an auto loader.

Jpach
11-18-2009, 2:19 PM
The two barrels I will be ordering from Krieger will be 18" for shorter stuff and 22" for longer stuff.

Not that anybody trully cares but me, but my AR-10 forward assist BCGs arrived today.:cool2: That means I finally have the bolts to send to Krieger to have the barrels made.

Thats badass. If you dont post pics of the guns and the stupidly tight groups the moment you reveal that the rifles are complete, there will be hell to pay :p

C.G.
11-18-2009, 3:00 PM
Thats badass. If you dont post pics of the guns and the stupidly tight groups the moment you reveal that the rifles are complete, there will be hell to pay :p

I am not sure what the Krieger's lead time is for barrels, but I am sure it will be a while, plus I still am saving pennies for the handguards, probably DD for the 18" and V-TAC for the 22", subject to change.

ar15barrels
11-18-2009, 10:38 PM
21 inch, 11 P5 Schneider.

Winner winner, chicken dinner...
Make it a medium profile forward of the gas block instead of a bull barrel.

Army GI
11-19-2009, 7:20 AM
Tell us more about what you want to use it for. If its just a plinker or hunting gun, 16-20" is fine. If you want to shoot to 1K year round 26"+ is the way to go. When I finish my AR-10 Palma rifle it will rock a 33" krieger.

I must see that.

WeekendWarrior
11-19-2009, 7:32 AM
WWRTW