Do longer gun's barrel improve accuracy?

Question

I have been reading a lot about guns in Wikipedia. I know much of the terminology of firearms. However, I was wondering why some firearms such as shotguns and rifles have very long barrels opposed to small handguns such as revolvers and pistols, that normally have shorter barrels.

I know, there are functional differences between the types of weapons I described: Shotguns normally shot shogun shells with pellets, Rifles have "rifling" inside their barrel, pistols are made to be held with the hand without shoulder support, revolvers have a cilynder of cartridges that rotates. (This descriptions is rough and doesn't intend to be a very accurate defintion of every gun type).

Nevertheless, shotguns rifles and snipers normally have longer barrels than pistols and revolvers (althought there are handguns with long barrels).

Here there is an article about the subject

The question is: What advantages and disadvantages come with differences in length of the barrel? And does a longer barrel improve accuracy?

I have made up some hypotheses. I list them here. :

-Longer barrels are used for higher explosive ammo because the barrel can contain the expanded gases and made them push the bullet over a longer barrel, giving the bullet more energy.

-Longer barrel means the sight is further and thus one can make more precise shots because the two aligning marks are further, and thus in order to seem aligned to the eye they have to be in "more aligned" than with a shorter barrel.

Answer 1

The short answer: Yes, a longer gun barrel improves accuracy. Theoretical accuracy of handguns and rifles is driven by rifling, barrel length, and bullet mass.

• Rifling: When the bullet travels through the barrel, the rifling (helical grooves in the barrel) forces the bullet to spin by converting some of its forward kinetic energy to angular momentum. This gives the bullet gyroscopic stability. Remember, a gun without rifling is a musket - without spin, the bullet trajectory is unstable, like a 'knuckle ball'.

• Barrel length: A longer barrel extends the time time interval where chamber pressure acts on the bullet's mass. Therefore, a longer barrel increases the exit velocity of the bullet and the effective range of the bullet. Friction limits the allowable barrel length.

• Bullet mass: Increased bullet mass increases the bullets inertia (resistance to external forces). Therefore, the bullets trajectory is less effected by external forces such as cross-winds or contact with obstacles (like brush, etc.).

Note that these factors are interrelated. Rifling is a function of barrel length (Twist per Length). So a longer barrel (rifle) imparts more spin to the bullet than a short barrel (handgun). But exit velocity also depends on bullet mass and barrel length. The bullets exit velocity and stability (its effective accuracy) depends on rifling, barrel length, and bullet mass. (Common calibers and their respective rates of twist are listed here).

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Standard shotguns do not have rifling. Their accuracy is more relative because they shoot multiple projectiles. Longer barrels create a more focused scatter shot than shorter barrels. The focus of the scatter is commonly modified with chokes.

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A few practical considerations:

• Sight radius: For a gun without an optical scope, a longer sight base increases accuracy. Misalignment errors by the shooter are reduced from trigonometry between the front and rear sights. However, long distance accuracy demands minute angle corrections only possible with optical scopes - the length of sight base is irrelevant.

• Heat strain: Gun barrels often get very hot from high energy rounds and high rates of fire. As a result of temperature differences, the barrel deforms/bends - therefore, the accuracy changes from the first shot to the last. To minimize heat strain and deflections, free floating barrels, and/or larger diameter (or fluted) barrels are used to maintain accuracy.

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Ultimately, there are advantages to each type. Hand guns excel at close ranges where maneuverability and rate of fire is critical. Shotguns dont require absolute accuracy to hit the target (an advantage when shooting at moving targets like birds) but have a very limited range. Rifles offer the best accuracy and range but reduced manueverability and often reduced rates of fire (depending on the action: Bolt vs Semi-Auto vs Full-Auto).

Answer 2

Something I would add to theNamesCross's answer:

Barrel length provides extra velocity, which as name's said improves accuracy basically directly. There will be less drop and less wind drift.

More powder could also be used, but there are limits, due to the maximum chamber pressure, maximum burn rate, and the speed of sound inside the combustion gas. Also heat and barrel wear would be increased.

So why do guns rarely have barrel lengths longer than say.. 24in? The reason is that there is are dramatically diminishing returns as the barrel length extends beyond 8 inches or so. If you check out the link Chris posted, you'll see that for a .308, the difference in velocity between a 16in and 20in barrel is only about 6%

So why don't most guns have stubby barrels?

1. Legality. In the US rifles must have a barrel longer than 16in, or the become classified as an evil "short barrel rifle". These require a lot of paperwork to legally obtain.
2. On a rifle, a barrel shorter than 12in may not have any advantage, since some space will required for a shooter to grip the rifle anyway.
3. A longer barrel can add weight, and act as a stabilizer. Thereby increasing accuracy, even if the ballistics are not improved.

Based on the above, is fairly clear why most guns are the length they are. Rifles will usually be 12-16in, going up to 20 in extreme cases.

Pistols have some other considerations. 1. They have to be light, so the chamber pressure is limited due to material strength. And 2. The barrel can't practically be longer than 6in or so. To get a good velocity out of a short, low pressure barrel, pistols use larger diameter bullets. These have more area for gas to push on so they accelerate over a shorter distance. This is ballistically disadvantageous, but it's not really an issue because pistols are designed for close range anyway.

Answer 3

Also, for accuracy, the quality of the bullet or projectile - if it is "out of balance" ie the centre of gravity does not coincide with the axis of rotation then it will "fly off" or miss its intended target. And if you want a reference try "The bullet's flight by F. W. Mann" long out of print though.

Answer 4

The article below refutes theNamesCross' short answer.

https://www.thetruthaboutguns.com/the-truth-about-barrel-length-muzzle-velocity-and-accuracy/

Look at the charts and you will see that bullet quality probably has more of an effect on accuracy than barrel length. But, it can also be seen that the shorted the barrel gets the greater the accuracy/repeatability of the shots. This is due to shorter length barrels has less "barrel whip" than longer ones.

Answer 5

A longer rifle barrel is not more accurate. The sight radius is longer (with iron sights and not a scope) which is better for the shooter to get a more accurate aim. Increased accuracy in a longer rifle barrel is a myth. There are many factors that affect accuracy in a rifle but barrel length is not one. Many get accuracy confused with windage, bullet drop, and velocity.

Answer 6

A rifle barrel that is long is always good that help shooters to get accurate aim.

Answer 7

I believe the longer barrel is more accurate in all calibers. I think the longer barrel helps hold the twist longer for better accuracy down range.