How long is too long for a .308 Win barrel?

[Varminterror]

“The Truth” is that 2,390fps is painfully slow...

 

[Nature Boy]

In fairness - Palma guys are shooting 32” 308wins, and doing so for a reason.

And F-T/R guys are running 30”

 

[lysanderxiii]

Bore or groove?




I'll just leave this right here.

The Truth About Barrel Length, Muzzle Velocity and Accuracy




GR

Caliber, when used as I did, is always bore.

 

[Nature Boy]

Thanks THR, this rifle I'm considering would be strictly for bench work. I would plan on re-barreling it when the time comes so I could make any adjustments then, I just don't want to spend time and components shooting out a handicapped barrel to start with is why I asked the question.

I went with 26” on my .308 target rifle with a MTU contour. When I ordered it I got it for the same purpose you’re looking for. Not gimped in the least and very competitive when shooting 600 yard F Class matches.

Pushes 185g Berger Hybrids at 2,720 FPS

 

[taliv]

the long barrels making bullets slow down is a practical myth. Even in pistol cals you still see gains at 20 inches in most cases. You loose your leaps after about 12 inches in most calibers anyway, and from there is just how much do those little gains mean vs how much length do you want. 24" will be about optimal as long as its not too long for taste. I know 26" feels too long in a bolt gun for me, under 21" feels to short. 21-24 would be my idea of perfect.

i wrote this in 2014.

with both Reloader 17 and H4350, shooting berger 140 VLD and hybrids, my 260AI starts losing velocity after about 26". my 28" and two 29" barrels were all slower than my 25" and two 26" barrels. I just put the 7th barrel on and went with 25" again. All 7 are bartlein 8.5 twist.

before i finished, i went through 13 260AI barrels, and at a given length, they were pretty much the same speed, but the 25" ones were all faster with same load than the 28,29" ones.
i know it keeps speeding up in 308 out to 32" and cannot explain why my experience was consistently different

 

[troy fairweather]

i wrote this in 2014.


before i finished, i went through 13 260AI barrels, and at a given length, they were pretty much the same speed, but the 25" ones were all faster with same load than the 28,29" ones.
i know it keeps speeding up in 308 out to 32" and cannot explain why my experience was consistently different

i all depends on the powder burn, the slow powders will gain more fps with a longer barrel.

 

[taliv]

i believe that too, based on reading powder load data, but don't have proof.

 

[mustanger98]

I was just remembering that the Israelis, back when they issued K98's, used 7.62NATO-chambered 23" barrels. I don't really know about accuracy on those, but I've heard .308 shoots close to the sights. I've wondered about how close as the range is extended and the sight elevated.

 

[Wreck-n-Crew]

The 308 is a great round but it's limits or shortcoming make it less ideal for long range shooting out to 1,000 yards. It is a great hunting or service round that packs a punch within 800 and much better at 600 or less. But barrel length makes a difference. Especially with good bullets and good powder. Bullets have come a long way and because of their progress the 308 is more capable. How much more is still debatable and trying to use a 308 for 1,000 yard shooting is still pretty challenging.

The 308 can and has made it to 1,000 yards without going through the transonic barrier around 1340FPS in a 24" barrel, yet it's just not any off the shelf ammo that can be trusted to do the job. This is more of a handloading job that doesn't to exceed SAAMI specs in pressure to do it. The transonic effect degrades accuracy

Many people have read this https://rifleshooter.com/2014/12/30...ato-barrel-length-versus-velocity-28-to-16-5/ and other related content only to assume a 308 becomes inadequate for 1,000 yard target yet the test doesn't tell the whole story.

The truth is barrel length, powder, and bullet choice make the big difference. Slower powder will give you more push and velocity than a faster powder and that applies throughout the gun world from pistols to rifle. The longer the barrel the more the push if there is enough powder capacity in the cartridge to get there. Though every cartridge is still limited by case capacity and barrel length becomes useless beyond a certain point.

Since 308 is one of those smaller capacity cartridges (for its bore size) that needs help to get to 1,000 with enough velocity to not lose accuracy before it gets there. It needs three things to make it more successful( really 4 to do so successfully and repeatably). A long enough barrel and a slow enough powder with the right bullet weight.

Then there is the BC of the bullet . You could say this is a fourth thing needed. Without a good BC (ballistic Coefficient) to cut the wind the bullet will bleed too much velocity before it gets there. Granted you can go through transonic flight and end up subsonic without good BC but then the accuracy tends to degrade substantially and bullet stability goes south. Not to mention fighting the wind which a fat bullet going that slow effects a 308 a lot. When you get past 500-600 yards the wind effect increases POI with increasing effect.

Then there is the issue where velocity meets accuracy. Getting the velocity that makes the 308 more capable doesn't mean you get the accuracy you need as any hand loader for accurate rifle can tell you. You need a level of precision that will average 1 MOA or better to get there reliably and if you want to get there accurately you will need both to fall into place. That doesn't always happen on the upper end of the velocity capabilities of just any slow powder and any low BC bullet of usable weight. A loader has to find one that works best with the combo and still have a small enough ES/SD to still hit within a reasonable margin at distance. A deviation of just 50 FPS and you leave the zone.

This is where the barrel length comes in and closes the deal. If you have enough length to utilize the powder charge then you can find that accurate load while maintaining the velocity best suited for long range accuracy.

If all anyone wants to do is hunt and maintain good energy out to 5-600 on bigger game then barrel length is not going to matter as much, An 18" barrel will easily fill that role. Just look at how popular AR-10 and the 20" Savage Hog hunter in 308 has become for hunting.

 

[FL-NC]

The key component is knowing the MV and applying the data. 24 is fine on a bolt action rifle like a M24 (700) but becomes rather lengthy on an AR10, where a 20" serves better. These are the lengths used on standard issue military sniper systems. For a rifle that wears a suppressor, I prefer 20" for a bolt action and 16" for an AR10, to minimize overall length. 16" Larue OBR's have won Special Ops sniper matches a few times.

 

[Walkalong]

i all depends on the powder burn, the slow powders will gain more fps with a longer barrel.

i believe that too, based on reading powder load data, but don't have proof.

I can prove it with 9MM and 5" and 16" barrels, and have posted the results a few times. I wasn't trying to prove that, I was just chronographing different loads.

Ballistics work the same for rifle calibers, it just takes longer barrels. It should not be hard to prove if one wanted to. The faster powder will hit peak pressure faster/sooner and cannot get the FPS the slower powder with a heavier charge (More energy) can. At some barrel length this will show up. Sounds like 25" for the .260 AI and whatever powder/bullet combination it was.

 

[taliv]

Walkalong are you saying with a fast powder that you got a slower velocity in a 16” bbl than your 5”?

 

[Charlie98]

it all depends on the application you will be using the rifle for. for tactical purposes, I'd say a 24" is about right. for hunting purposes, around a 20". for bench or prone shooting, I've seen from 24-32" barrels. and regardless of what some have previously said, the longer barrels do boost your velocity, using handloads, and in 1000yd gr match, the 308 needs all the speed it can get!

That's correct. The .308 starts to run out of gas at 800-1000yds, load tuning and barrel are critical.

I've got a 24" Savage bolt gun set up as a tactical rifle, it does well enough out to 700yds (as far as I've been able to shoot it,) but I could see where it was starting open up. FGGM was consistent enough, but my handloads (not tailored to the rifle...) started to have problems by the time I got out to 700, using 168grn Noslers.

Contrast that with my Springfield Socom16 (16" barreled M1a) which I don't shoot much beyond 300yds... a product of the sights and the barrel length.

 

[Nature Boy]

The .308 starts to run out of gas at 800-1000yds, load tuning and barrel are critical.

Every cartridge starts to run out of gas the moment it leaves the barrel, they all benifit from load development and selecting the right combination of barrel length/twist for the application is critical.

The .308 not being unique here.

I’ve been shooting a 6BRA and the consensus from others that have been shooting it for a while in long range BR, including gun smiths and competitors (some world record holders) is that 27”-28” is the optimal barrel length. Anything longer makes it more difficult to tune and provides no benefit.

Back to the 308. Guys and gals who shoot it in long range F/TR, and are competitive, gravitate toward the 200g Berger in a barrel chambering to accommodate the longer bullet with a twist and length designed to milk all the available BC from it.

And generally speaking, they run either H4895 or Varget. Slower powders don’t seem to work well. There’s just not enough case capacity in the .308, which is it’s primary limitation.

 

[Wreck-n-Crew]

Walkalong are you saying with a fast powder that you got a slower velocity in a 16” bbl than your 5”?

No. He got higher velocities with slower powders in a carbine than he did the faster powder. Even a faster pistol powder in 9mm will produce more velocity in a 16 barrel than a 5" pistol barrel. I did some testing I did myself and posted the results with 9mm using 4 different powders, a full size pistol, and a 16" Carbine about 3 years ago found here …. https://thehighroad.org/index.php?t...-vs-factory-chrono-test.799017/#post-10190193 showed much higher velocities with slower burning powders in a carbine.

I used fast powders and slow powders and some in between. Fastest powder was Red Dot and slowest powder was Power Pistol. If you look at the burn rate chart https://www.hodgdon.com/wp-content/uploads/2017/09/burn-rate-color.pdf that Red Dot is near the top of the chart (#7) and is a relatively fast burning powder and Power Pistol on the slower end (#35) . Other charts vary a little but they are relatively accurate as some powders burn at the same rate and may be just above or below another on the list.

 

[Wreck-n-Crew]

And generally speaking, they run either H4895 or Varget. Slower powders don’t seem to work well. There’s just not enough case capacity in the .308, which is it’s primary limitation.

Just to add: there are several powders on the rifle powder list and as Nature Boy said the slow ones are not good for smaller cases. But for the ones that do work in 308 they are closer to fast up to medium for rifle powders. Varget for a 308 would be considered a "slower 308 powder" but not a slow "rifle powder".

The same goes for magnum pistol rounds up to the smaller rifle rounds with less capacity. Power pistol is a slow powder for 9mm but not for 44 Magnum where H110/W296 is a slow pistol powder not useful in several smaller (non Magnum) pistol cartridges.

Then there are crossover powders Like IMR4227 which works in Magnums and small rifle cartridges like 300BLK and 7.62x39. And Red Dot which works in Shot gun up to 10mm in pistol cartridges. The list goes on.

 

[Derek Zeanah]

Lots of good replies here. This is my anecdote:

I bought a Remington 700 with a 24" 5R barrel and had these guys do their barrel treatment on it back before they became AR only. It's kind of weird - the barrel was thinned a bit and a jacket was put over it, and in between they filled it with some new high-tech polymer that conducts heat better than copper, but directionally (maybe it's multiple layers with different conductivity?) They had me empty a mag from an AR quickly then shove my finger into the chamber, which was room temperature and covered with carbon dust. The outside of the barrel jacket was scorching hot, on the other hand. Weird, and cool, and apparently of limited interest/application. My assumption is that barrel rigidity went way up as part of this.

Anyway, as part of they process they cut the barrel back to 20", and I took that to Thunder Beast Arms for a long distance course. Shooting 175gr 7.62x51 Federal Gold Medal Match in Wyoming the longest first round hit on a 10" plate was at 1,080 yards.

To me that's plenty, and the additional gains I'd get from a longer barrel aren't necessarily worth the trade-offs in balance in weight. At least, not in a .308.

 

[Walkalong]

Walkalong are you saying with a fast powder that you got a slower velocity in a 16” bbl than your 5”?

My N320, 124 Gr plated bullet 9MM load basically gets the same FPS from a 16" barrel as a 5" barrel. 1050/1075ish FPS.

I assume the N320 load gets faster than 1050/1075ish somewhere in the barrel (Between 5" and 16") and then slows back down some, basically gaining nothing.

Slower powders like N340, AA#5, HS6, WSF, etc gain velocity from the longer barrel.

I have a lot of data with 9MM loads shot from 3", 4.5", 5" & 16" guns on the same day/time.

 

[Walkalong]

Here is one where it lost some FPS in the small 5 shot sample.

3.9 Grs N320, 124 Gr plated bullet, CCI 500 primer, 87 degrees, 77% RH. 7-2017

3" S&W Shield 5" Colt Series 80 16" RRA AR
HI 955 HI 1076 HI 1070
LO 918 LO 1042 LO 1006
AVG 932 AVG 1057 AVG 1033
ES 37 ES 34 ES 64
SD 12 SD 13 SD 23

 

[Walkalong]

You can see that much difference in two 5" barrels sometimes. Same 3.9 N320, different 124 Gr plated bullet, S&B primer.

3" S&W Shield 5" Colt Series 80 5" S&W Pro
HI 905 HI 1066 HI 1104
LO 869 LO 1025 LO 1030
AVG 885 AVG 1048 AVG 1061
ES 36 ES 41 ES 74
SD 14 SD 13 SD 27

 

[Walkalong]

3.9 Grs N320, 124 Gr plated bullet, Fed 100 primer, 83 degrees, 35% RH. 5-2016

3" EMP 5" S&W Pro 16" RRA AR
HI 977 HI 1073 HI 1091
LO 937 LO 1038 LO 1037
AVG 957 AVG 1055 AVG 1066
ES 40 ES 35 ES 54
SD 14 SD 13 SD 18

 

[Walkalong]

Use a fast for .308 powder and a slow for .308 powder and at some barrel length it should show the same thing, the faster powder can no longer take advantage of the extra length.

But the Palma guys are not shooting fast for .308 powders. I doubt the F Class, PRS, etc folks are either.

 

[alsaqr]

Many years ago i had an revamped 1898 Mauser with an 18" barrel in .308 Winchester. Too darn loud and it soon went away. My most accurate .308 is a Remington 700 with a 26" barrel.

308’s don’t kick much anyway, but a 18lb 308 that has a good muzzle brake I very pleasant to shoot and the lack of recoil can help you be a more consistent shooter

Yep, an 18 pound .308 should have little noticeable recoil.

 

[Charlie98]

Every cartridge starts to run out of gas the moment it leaves the barrel, they all benifit from load development and selecting the right combination of barrel length/twist for the application is critical.

The .308 not being unique here.

I'm not talking about strictly velocity... there is also the transition to sub-sonic and other factors. In the .308, you are limited by chamber dimensions to, basically, sub-200grn bullets (and that's pushing it) and the corresponding length.

 

[Nature Boy]

I'm not talking about strictly velocity... there is also the transition to sub-sonic and other factors. In the .308, you are limited by chamber dimensions to, basically, sub-200grn bullets (and that's pushing it) and the corresponding length.

Not many 308 loads that are loaded to reach 1,000 yards have this problem so I don’t understand what your point is. Even moderately loaded, factory loads in .308 are supersonic past 1,000.

Keep the OP in mind. He’s talking .308. Let’s not let this devolved into “X cartridge is better than Y cartridge” crapfest, OK?