Gun-ology: The Myth of the Longer Barrel


We have all heard it… The longer the barrel the more accurate the gun. We have all seen the movies – the “shooter” carrying a gun with an impressively long barrel and sniping at 1000’s of yards.

So we need long barrels, right?

Wrong!

It is a myth you need a long(er) barrel to be more accurate. Actually it is a bunch of myths. I have fallen for it, you may have too.

Let me separate myth(s) from truth.

First and foremost, a longer barrel doesn’t make a gun in-and-of-itself more accurate. It doesn’t “stabilize” a bullet more, making it more accurate. It isn’t (normally) required to get the full explosive “charge” (of the powder) behind the bullet. It doesn’t give the bullet more “time” to stay pointed or aimed at the target.

All of these are inaccuracies often heard in the shooting and hunting community.

What does a longer barrel do?

The main thing a longer barrel does is to slightly increase the velocity of a bullet. In fact for most calibers, you can subtract 50 – 80 fps (or less) for each inch of barrel less than the 26 inches. Why 26 inches? A 26″ barrel is what is used by most barrel and ammo manufacturers as a standard for measuring muzzle velocities (which is what is quoted for instance on ammo boxes).

But wait… Chief GAGG, that can be 500 – 800 fps lower velocity than a 16″ barrel!!

Good math grasshopper.

Average Velocity Loss Per Inch for .308 Winchester. Source rifleshooter.com (http://rifleshooter.com/2014/12/308-winchester-7-62x51mm-nato-barrel-length-versus-velocity-28-to-16-5/)

Average Velocity Loss Per Inch for .308 Winchester. Source rifleshooter.com (http://rifleshooter.com/2014/12/308-winchester-7-62x51mm-nato-barrel-length-versus-velocity-28-to-16-5/)

First, most ammunition doesn’t loose that much per inch of barrel. Take for instance the very popular .308 Winchester caliber. The chart shows that on average it looses 20-26 fps. So the loss between a 26 inch barrel and 16 is only 200 – 250 fps.

Also very few people shoot or use 26 inch barrels on a gun.  A 26″ barrel is typically a heavier barrel profile that results in front heavy guns. Most guns utilize an 18 – 24 inch barrel. So even if you have a worse case scenario of a higher per inch loss, like 50 – 80 fps, then you are only talking about a 400 – 650 fps difference.

The loss in velocity alone does not change the initial accuracy of the bullet. As a bullet drops in velocity below its stabilization point (varies per caliber), its accuracy begins to suffer. For most larger caliber rifle rounds this is well beyond 600+ yards (note I say most). The longer barrel giving a bullet higher velocity therefore pushes the stabilization drop further downrange. For the average hunter and sporting shooter who is shooting under 600 yards anything over a 16-18 inch barrel is wasted weight you carry. Remember a barrel is a lever arm, and if you add 2 inches of barrel which weighs an additional 4 ounces, one is actually adding 1/2 – 3/4 lb of actual weight (try the math here).

Personally on my “working” guns I stick to a 16 inch barrel unless there is a caliber-specific-ballistic reason to do so differently. Rounds like the 6.5 Grendel have specific barrel length needs – you wouldn’t want anything less than a 24 inch barrel if you want to take full advantage of it. My 300 Win Mag has a 22″ barrel, but I have shot 18 and 20 inch barrel versions. Shooting those calibers in shorter barrels, however, does not necessarily mean loss of “accuracy”. Conversely calibers like the 300 Blackout suffer very little in ballistics even with barrels as short as 9″.

Know your caliber ballistics, but a 16″ barrel is a good starting point that balances ballistics to weight (and sometimes budget). Why 16″? Well first and foremost it is the legal length you don’t have to permanently attach a muzzle device (which I hate doing) on firearms like AR-15. Second most barrel makers make the most variations in barrel profiles in the 16-18 inch lengths (pencil, recon, standard, fluted, bull…) – so you can pick the weight profile you want. Once you get beyond an 18 inch barrel a lot of manufacturers start to reduce the variations. Mostly you find only the heavier profile barrels beyond 18 inches. Don’t forget the lever arm effect of the added length/weight. For working or hunting guns, that lever arm effect means a lot of fatigue over a day of shooting/hunting. If you don’t think so, take an 18 inch rod and hang a half pound weight on it – see how long you want to do that. Finally, from an economy of space, I like the 16 inch gun build profiles. The guns are compact easy to move in tight spaces, store/hang better in gun cabinets, racks, etc. And are generally more efficient in movement.

And don’t forget the cost. Typically barrels beyond 18 inches go up in price significantly.

Back to those myths:

  • It is the twist rate of the barrel (along with sufficient barrel length to impart the spin) that stabilizes a bullet. Know the specific bullet weight/twist rates required for the round you are shooting. Generally there are  twists ratios that are known to best stabilize a wide range of bullet weights in a caliber.
  • Most barrels 16″ and longer allow the full “explosion” of the charge to develop behind the bullet. There are a few calibers that require longer barrels to make that happen, but it is really only when you start going to shorter barrels (like 12″, 10″…) that you do have some issues with the full force affecting the bullet.
  • As far as keeping a bullet “pointed” – complete horse hockey. In fact, pragmatically since no person keeps a barrel completely still during a “shot” a long barrel would have the inverse effect and potentially allow a person to accidentally move the aim point off the target as the bullet is in a longer barrel longer than a shorter barrel.
  • Longer barrels do tend to be heavier barrels and generally have more “steel” to more uniformly heat as multiple rounds are fired through it. That said if you are shooting a barrel a lot, then you can get a bit heavier barrel profile to accommodate this need.
  • Sometimes longer barrels help with barrel harmonics. However, the physics behind barrel harmonics is so complex simply saying a longer barrel can give better harmonics is not accurate. For instance simple variations in the steel in the barrel can disrupt harmonics.

Hope this clears up some of the myths of “the longer barrel”.

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