First, longer barrels are NOT more accurate. Interestingly enough if we are discussion barrels of the same diameter, rifling, chamber, etc. the shorter barrel will be stiffer. The stiffer barrel will be more consistent, thus more accurate.
So why so many long barrels? Barrel length is required for the expanding gas from the powder charge to accelerate the bullet before exiting the muzzle. Once the bullet exits the muzzle there is no more force accelerating it, and only air attempting to slow it down (drag). For a long range shooter speed is a good thing. The faster the bullet is moving the less time there is for the wind to act upon it. If you pull up a ballistic calculator and punch in your favorite load, take a look at what happens to the wind correction when you increase the muzzle velocity.
So, this seems to indicate that long range shooters should go with the longer barrel, right? Not necessarily. You have to have a load that needs the longer barrel. Otherwise you are just carting around extra weight and a longer pole to run into stuff.
At the Indiana Law Enforcement Academy (ILEA) Advanced Observer/Sniper Course students shoot out to 1000 yards. I attended this course with my 26" barreled Remington 700. My partner was also there with his 20" barreled Remington LTR. Both barrels are made on the same machinery with the same type of rifling and the same chamber reamer specs. We were both shooting the same lot of 168gr Federal Gold Metal Match ammunition. At 900 yards, both of us were punching nice round holes in the target. This means the bullet was still stable when it passed through the target backer. When we moved back to 1000 yards, BOTH of us were getting "keyholes" where the bullet passed through the backer sideways. This indicates that the bullet has gone transonic prior to hitting the target and has begun to tumble.
What does this tell us? It demonstrates that with this factory load 6" of barrel makes absolutely no difference at 1000 yards. 6" of barrel will make a difference carrying it through the woods, abandoned houses, vehicles, building maintenance rooms, etc. I have also found out the hard way that a 26" barreled rifle in a Pelican 1750 rifle case will not fit in 90% of the rental cars out there.
The next question I usually see is "Will the shorter barrel stabilize the bullet?" Length does not stabilize the bullet. The barrel twist stabilizes the bullet. I am sure there is a length you can get to where you have so little rifling that the bullet is not stabilized. However that length would be well below the legal length for a rifle in the US. If you start looking at building a 4" .308 pistol you may want to do some more research. A factory Remington 1:12 twist .308 barrel will stabilize most of the commercial cartridges available. Many have reported good results with the 208gr Amax bullet through a 1:12 barrel. This is well outside of what most beginning shooters will be sending downrange. If you plan on shooting bullets on the heavy end, then look at a 1:10 twist for the .308.
So in conclusion, unless you have a specific situation in mind a 20" .308 will be sufficient for most long range shooting. If you are hand loading and want to get the most out of a long range load, then the 26" barrel may be a better choice. Length does not equate to accuracy. Length only gives you more velocity if the powder charge is large enough to take advantage of it.
If you are a long range shooter who hand loads, get the 26" barrel. If you are a police officer shooting a factory load, you can probably get away with as short as 16" if you use a good flash suppressor. 18-20" will be about perfect. If you are like me and use one rifle to do everything, then the benefits of a 26" barrel outweigh the drawbacks from the weight and overall length.
Hopefully now I can just link to this post when the next thread appears.
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