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Posted: 3/17/2012 4:17:34 PM EDT
| What is the difference in accuracy between 16", 18" and 20" .308 barrels? I’m getting ready to order an OBR from LT and am leaning towards the 18” barrel as I will typically use this rifle for 100 - 300 yard shots with an occasional 600 yard shot. I like the versatility of the 18” barrel but thought I would check with the group and see what they think about barrel length before making the investment. Thanks. |
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Accuracy and barrel length are driven by barrel time, or the timing of the shock wave that travels through a barrel from chamber to muzzle at over 28,000 fps. Time your bullet's exit with the shockwave when it's at the chamber (away from the muzzle), and you'll see better accuracy. Longer barrels have longer windows for optimum barrel time, with more gradual curves for accuracy nodes.
Then combine that variable with barrel whip, and you have another factor. Longer barrels whip more, diameters being equal. I think 18" is a great length to go with for an OBR, since you won't have as much muzzle blast as a 16", the gun is still plenty maneuverable, and you get decent velocities. I doubt you would see any real differences in accuracy between the 3 lengths in that platform. |
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Quoted:
What is the difference in accuracy between 16", 18" and 20" .308 barrels? I’m getting ready to order an OBR from LT and am leaning towards the 18” barrel as I will typically use this rifle for 100 - 300 yard shots with an occasional 600 yard shot. I like the versatility of the 18” barrel but thought I would check with the group and see what they think about barrel length before making the investment. Thanks. "Accuracy" is a loaded term. 
I don't think length is really the deciding factor on accuracy. Get a quality barrel and you can have accurate shot placement with any of those lengths. That said, many shooters consider shorter barrels to be more accurate than longer ones due to less whip. On the other hand, a quality barrel will address that, too. FWIW, I have an 18" stainless bull barrel on my DPMS SASS. It's more accurate than I am and I can cloverleaf Federal Gold Medal Match 168s at 100yds all day long. I routinely take it to long range shoots and consistently hit targets out to 820yds. (This rifle really likes FGMM 168s - much more so than the 175s.) I think velocity is going to be your primary factor. Most factory loads tend to burn their powder in the first 20". Velocities for factory loads from my 18" barrel average about 100fps slower than advertised. A 16" barrel will be even slower which will affect your ability to put shots on target at longer ranges if there's any wind on the shot. My opinion is the 18" barrel is a good compromise between weight, maneuverability, and velocity. I think you can have accurate barrels at any of the lengths you listed. |
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This is an often repeated topic, but I will say there is always something to learn here. From a lot of reviews in mags, here, etc., it appears the 18 inch tube has the best of everything, and is the optimum (meaning you don't pay as big of a velocity penalty down from a 20 inch barrel, at least with 168-175 projectiles). I believe most manufactures show .308 velocities out of 24 inch barrels.
16 inch barrels see a little more loss, but not unreasonable. Anything below 16 inch apparently starts chopping away significantly at the .308 cartridge. It should also be noted, that I have read the .308 is more efficient than the 5.56, and I believe it has to do with caliber and powder burn rate/efficiency. |
| I also agree that an 18" will probably serve you best. I have a 18" DPMS and hold MOA out to 700yds if i'm doing my part. The only thing you lose with the shorter barrel is velocity. So if you plan on stretching this rifle to it's limits, which 600yds isn't, then 18" should be just fine. When I was looking at the .308's I was told here that the .308 round is fully stabilized at 18". So take that FWIW. |
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Quoted:When I was looking at the .308's I was told here that the .308 round is fully stabilized at 18". So take that FWIW.
That advice is worth what you paid for it. There are several variables at play with stability and barrel length is not one of them. It is a contributor to one of the variables, velocity, but you can't say that the bullet is fully stable in X length barrel and speak with any level of credibility. For a particular caliber bullet of a particular length, you need to spin it at a certain RPM to get it to be stable. With a barrel of sufficient twist, you can get the bullet stable with any barrel length, because the barrel length is irrelevant. The .308 has a fairly large bore for its case volume and is a pretty efficient cartridge with regard to barrel length and velocity. Within the standard range of .308 barrel lengths, from 16" to 26", the total difference in velocity is about 300fps. Other than increased muzzle blast, there is nothing negative about the 16" barrel. The velocity difference isn't that great. Arguments will go back and forth on accuracy between the two but the individual barrel will determine that, not some theory about what effects the length has. |
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