Optimal barrel length for 308

kombayotch said:
Here is an article about the Houston warehouse: http://www.angelfire.com/ma3/max357/houston.html

The 21.75" figure was supposedly optimal for accuracy, not velocity. There is no such thing as "optimal length" as far as velocity goes, and there is no fixed value for velocity loss per inch. Both of these are highly dependent on the caliber and cartridge, in addition to the bullet and powder combination being used.

I chopped one of my 308 barrels from 26" down to 22". I only lost 20 fps. on my 190 SMK + 42.3 gr. Varget load, but a whopping 200 fps. on my 110 VMAX + 48.0 gr. Varget load. Why? Because the load with the heavier bullet had less powder and it was running at a higher pressure than the load with the lighter bullet. The burn was nearly complete in the 22" barrel, but it wasn't for the lighter bullet load. Similarly, take two loads with the same bullet running at the same velocity, but using powders with very different burn rates and start chopping down the barrel. The load with the faster burning powder will maintain most of it's velocity down to a shorter length than the load with the slower burning powder. It requires less barrel length for a complete burn. This idea that a 24" 308 barrel is required for long range is decades old and was based on the bullets and powders available at the time. It's probably based on a single load. Technology has changed, we have more efficient powders and bullets with higher BCs.

Talk to a bunch of guys shooting 155's with Varget and ask them what their velocities are. The answer will most likely be somewhere between 2800-2950 fps. and where they are on that scale isn't proportional to their barrel length at all. You'll usually only get velocities over 3000 fps. from Palma guys running a 30-32" tube. Guys shooting the 175 SMK will give you a velocity between 2600-2750 most of the time, again with no relation whatsoever to barrel length. When you ask them why they shoot it at that velocity, the answer is almost always: "well, I can run it up to X fps., but it shoots much better down here at Y fps.". And Y fps. is obtainable whether you're running 20" barrel or a 28" barrel. This guy was winning the US F-Class Nationals shooting the 175 SMK at 2610 fps.: http://www.6mmbr.com/gunweek031.html You can easily hit that node with a 20" barrel. What F-Class barrel lengths are winning is irrelevant. Most people are getting longer barrels because they've always been told that they need a long barrel to be competitive. Then they run them at nodes that you can hit with shorter, stiffer barrels...

A few inches of barrel length has a lot more effect when you're using factory ammo, not as much with handloads since you tend to tune them to nodes vs. running the same charge weight for every gun.
Click to expand...

Thanks!!
THAT was the article I was mentioning. I had it bookmarked in my last computer, but not this 1, until now.
 
AlexF said:
Good evening, let me start by saying that I'm honored to have an expert from Alberta Tactical Rifle reply to one of my posts even if it's to confirm that I'm wrong.
I do agree with the point that you don't need a long barrel for 308 to work well but the question is: what is the optimal length?
Can a shooter with a 21.75" barrel outshoot himself with a, say, 26" barrel?

Luckily at least one experimental answer is easy to find: look at what barrel length wins in world class F-TR competitions (I don't know the answer but will look it up).
The optimal barrel length has to be the median or average winning barrel length (or there is some hidden bias, always a possibility).

Regards,
Alex
Click to expand...

Alex
Certain competition persuasions have a bias towards short or long barrels that go waaaay back. Many of the known truths in the shooting sports may have been true in their time, but things do and have changed.

At 1 time variable power scopes were shunned as POI supposedly changed with magnification, apparently this is no longer the case as many winning competitors in a wide cross section of competitions now successfully win with variable power scopes.
Years ago longer barrels were required to attain the best velocities, but with improvements in gun powders, this is simply no longer the case.
In the past bullet BCs were much lower than today. The extreme long shots that are now common place were unheard of.

Many have not kept up with the changes and improvements in the firearms world.
To state that there is a significant loss in either accuracy or bullet velocity as a blanket statement is just not the case any longer.

We built 9, 308 caliber rifles that apart from colors and stocks were basically identical. All based on the same actions with sequential serial numbers, the same barrel specs from the same maker and all from the same lot of barrels and all with the same barrel lengths and chamber specs. The total variation in velocity between the rifles all being test fired with the same bullet, powder casing and OAL was about 100 fps. All the rifles shoot WELL under 1/2 MOA and all produce higher than what is considered normal velocities for 308 win while using only 21.75" long barrels.
 
Another very interesting article on the subject.

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

They seem convinced that for a . 308w a 20 and 18 inch barrel have no important lost in velocity.

To the one that i have choped a longer barrel to 20 or 18 inch barrel, what is the difference in muzzle flash ? In this article they have clear the problem with a suppressor, but for us ?
 
Charles said:
Another very interesting article on the subject.

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

They seem convinced that for a . 308w a 20 and 18 inch barrel have no important lost in velocity.

To the one that i have choped a longer barrel to 20 or 18 inch barrel, what is the difference in muzzle flash ? In this article they have clear the problem with a suppressor, but for us ?
Click to expand...
I have also been curious about increased muzzle flash/noise in a shorter barrel. I would think it would be much greater in Ruger's 16.5" barrels compared to a 21" or 22" barrel. Comments?
 
StoneHorse said:
I have also been curious about increased muzzle flash/noise in a shorter barrel. I would think it would be much greater in Ruger's 16.5" barrels compared to a 21" or 22" barrel. Comments?
Click to expand...

1 would think that building a 14" barreled 338 RUM would make the rifle a fire breating dragon. I know that what I thought when a client proposed just such a build. Shooting it last weekend was a surprise for me to say the very least. With factory Remington ammo there was no discernable flash, 1 hell of roar I will admit but no flash.
Who knew??
 
alberta tactical rifle said:
1 would think that building a 14" barreled 338 RUM would make the rifle a fire breating dragon. I know that what I thought when a client proposed just such a build. Shooting it last weekend was a surprise for me to say the very least. With factory Remington ammo there was no discernable flash, 1 hell of roar I will admit but no flash.
Who knew??
Click to expand...
Interesting. The big bang theory held true but flash protection not needed :D.
 
The Ideal Barrel For A .308 Caliber Tactical Rifle

Extremely interesting article by Daniel Lilja (Lilja Precision):

The Ideal Barrel For A .308 Caliber Tactical Rifle
http://www.riflebarrels.com/articles/longrange_shooting/ideal_barrel_308_tactical_rifle.htm

Another excellent but non-308 related article for 338 Maniacs ;)
Barrel Lengths and Velocities in the 338/378 Weatherby Magnum
http://www.riflebarrels.com/articles/bullets_ballastics/long_barrel_velocity.htm

I don't have winning F Class-TR specs but am still looking,
Alex
 
Not really interesting, actually. Yet another article where someone blindly chops down a barrel without any re-tuning of the load. Yeah, mimics what you get with factory ammo nicely, but not the situation you have with handloaded ammo. Unless of course you're the type of reloader who just choses the "accuracy load" from your manual and uses it blindly without doing any kind of load development of tuning...

Tell you what, find us an article where the barrel gets cut down and then the load gets re-tuned to keep it on the accuracy node the way it would actually happen in real life. Show us the velocity comparison in that situation.
 
To the OP:

Cut your barrel to whatever length you like best, be that 22" or 18" or 16" or 21.75" etc. There is surprisingly little difference, especially if your criteria for shooting it at longer ranges is "just for fun". If 20" seems "just right" to you then that is exactly what you should do.

A shorter barrel is louder (more muzzle blast), and it also puts the muzzle closer to your ears so it is a double whammy. For range use where you always have hearing protection this doesn't matter but I really would not want to fire a short barreled high power rifle as a hunting rifle.

For serious competitive use, there is a big difference between a .308 at 800 yards and an .308 at 1000 yards. At 800 yards everything works easily; if you want to be really competitive at 1000 yards you need to pay attention to every detail. No there isn't an invisible wall (hey I loved that graphic!! ;-) and I am sure that I could put together an 18" barreled .308 that is probably good enough to win a match at 1000 yards but there are a number of factors that tend to compound on you and work against you.

There is no single "optimal" length. If you want accuracy, shorter generally works in your favour (but, a good 30" match barrel is more accurate than the vast majority of shorter barreled non-match-barreled .308s). If you want a bit of extra velocity for whatever reason then longer is better (but the returns are impressively diminishing).
 
I wouldn't rely on old articles for the effectiveness of short barreled 308...
The ammo (especially the Hornady Superformance) is so much more advanced than anything in 70s, 80s and even 90s.
The Superformance 178 gr BTHP Match stays supersonic to 1275 yards from a 24" 308 according to Hornady. I believe you would have needed 300 win mag to achieve similar performance until recently...
The best thing is that the loss per inch is much smaller with the superformance ammo (I believe Hornady says something like 13-15 fps per inch).
With that kind of velocity loss you should be able to stay supersonic well over 1000 yards with 20" and even 18" barrel...
 
rnbra-shooter said:
To the OP:

Cut your barrel to whatever length you like best, be that 22" or 18" or 16" or 21.75" etc. There is surprisingly little difference, especially if your criteria for shooting it at longer ranges is "just for fun". If 20" seems "just right" to you then that is exactly what you should do.

A shorter barrel is louder (more muzzle blast), and it also puts the muzzle closer to your ears so it is a double whammy. For range use where you always have hearing protection this doesn't matter but I really would not want to fire a short barreled high power rifle as a hunting rifle.

For serious competitive use, there is a big difference between a .308 at 800 yards and an .308 at 1000 yards. At 800 yards everything works easily; if you want to be really competitive at 1000 yards you need to pay attention to every detail. No there isn't an invisible wall (hey I loved that graphic!! ;-) and I am sure that I could put together an 18" barreled .308 that is probably good enough to win a match at 1000 yards but there are a number of factors that tend to compound on you and work against you.

There is no single "optimal" length. If you want accuracy, shorter generally works in your favour (but, a good 30" match barrel is more accurate than the vast majority of shorter barreled non-match-barreled .308s). If you want a bit of extra velocity for whatever reason then longer is better (but the returns are impressively diminishing).
Click to expand...

I waited for a competitive shooter to cite some facts but remember this very important ballistic performance rule:
ballistic performance drops drastically when reaching transonic zone 1300-1500fps. (stay clear of the sound barrier)
you want high performance stay over this threshold area since drag climbs rapidly when velocity drops from 1500 fps to 1100 fps which means a large loss of velocity, a large increase in lag time (wind drift) and some bullet stability problems during the supersonic to subsonic transition.

This is the reason why 308 Win 175gr 2600fps performance take a solid hit at around 800 yards.
For the exact same reason, 338 Lapua Mag 300gr 2800fps performance take a solid at around 1500 yards.

You'll get better mileage if you're at high altitude and when the weather is hot but the basic principle is that entering transonic zone means a significant drop in performance because if rising drag.

Using a longer barrel give extra velocity which simply extend the time/distance traveled before reaching the transonic zone.
The bullet still works below 1300fps but you've taken a large performance hit which is not paid by the bullet which stayed clear out of it.

Alex
 
rnbra-shooter said:
To the OP:

Cut your barrel to whatever length you like best, be that 22" or 18" or 16" or 21.75" etc. There is surprisingly little difference, especially if your criteria for shooting it at longer ranges is "just for fun". If 20" seems "just right" to you then that is exactly what you should do.
Click to expand...

Jail is fun isn't it?
 
AlexF said:
I waited for a competitive shooter to cite some facts but remember this very important ballistic performance rule:
ballistic performance drops drastically when reaching transonic zone 1300-1500fps. (stay clear of the sound barrier)
you want high performance stay over this threshold area since drag climbs rapidly when velocity drops from 1500 fps to 1100 fps which means a large loss of velocity, a large increase in lag time (wind drift) and some bullet stability problems during the supersonic to subsonic transition.

This is the reason why 308 Win 175gr 2600fps performance take a solid hit at around 800 yards.
For the exact same reason, 338 Lapua Mag 300gr 2800fps performance take a solid at around 1500 yards.

You'll get better mileage if you're at high altitude and when the weather is hot but the basic principle is that entering transonic zone means a significant drop in performance because if rising drag.

Using a longer barrel give extra velocity which simply extend the time/distance traveled before reaching the transonic zone.
The bullet still works below 1300fps but you've taken a large performance hit which is not paid by the bullet which stayed clear out of it.

Alex
Click to expand...


That is also 'old school'. A bunch of Bullets today (and several from about 10yrs back) have no issue going subsonic and retaining superb accuracy.

Yes, wind drift will increase but not as dramatically as you may think. It's not like the bullet goes along nice and straight, goes subsonic, then blows over a bunch of feet. The increase of drift is quite predictable and can be accounted for.

Berger and others, wil be producing way more bullets that will be subsonic tolerant. The first ones I tried with success were the Amax.

Build, tune it, shoot it.

Enjoy...

Jerry
 
Oleg, the fellow that just won the DCRA Grand Agg in F-TR did so with a 32" True-Flite in 223. Now I will be the first to say that one agg proves nothing and it was not a 308 but I will take a long barrel any day over a shorty for long range!
 
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