Barrel Length: Longer Barrel = Accuracy?

Raptor937 SG

After reading a couple of posts at a firearms forum, that barrel length doesn't have any effect on accuracy, I started to wonder. Of course I'm not talking about a barrel so long that it touches the target Laughing .

I keep seeing this come up on gun forums all over the net and even here. I don't understand how a longer barrel could possibly give you more accuracy. As far as I can tell a longer barrel increases velocity but not accuracy. You may have to hold the sights a little higher with a 14.5" compared to a 20" but that doesn't mean it is less accurate. I've always been taught that accuracy is affected by barrel tension, rifling, ammo, bolt mechanism (?), and the shooter. Am I wrong or is this truly a common misconception in the gun community?

A few of the replies.

Depends on your definition of accuracy.

Longer barrels dont help precision but do help accuracy. Easier to get rounds nearer the target due to less drop at range (accuracy) but not smaller groups (precision). Here in the gun forums we call precision accuracy...

1) barrel length increases velocity, not accuracy per se.
2) longer sight radius is more accurate for a given shooter
3) use of optics negates sight radius
4) quality control of ammo (i.e. "match" grade stuff) will affect accuracy a lot more than bbl. length

So does a longer barrel make a weapon more accurate or is this a myth?

CenturionMBT SG

well, tell me which is more accurate, a smith and wesson or an M16

SMAPLionHeart SG

handguns are for short range...
You don't see snipers in movies using handguns for sniping accuracy..

handguns = shorter barrel..
sniper rifles = longer barrel..

LazerLordz SG

+ rifling.

nismoS132 SG

as mentioned in your 2nd quote.

a longer barrel increases the bullet velocity as well as put it that wee bit closer to the target. the higher velocity helps bring it to the target faster, and such also aids accuracy.

Moonstriker SG

right on target Laughing

touchstone_2000 SG

Yes longer barrel gives you better acurracy but there is a point of diminishing returns.

Soon the centre of gravity of the gun is in front and aiming it becomes a non trivial matter.

In addition you have to worry about warping of the barrel and cooling. As the gun gas takes longer to exit from mouth of the barrel, a lot more of the heat goes into the barrel. After a few shots the barrel may not be true. Why do you think tank guns have jackets?

tvdog SG

Accuracy depends on so many factors of a weapon, its ammo, its internal mechanisms etc.

But if we are talking about the barrel alone, then I think - yes, as a general rule, a longer barrel gives you more accuracy.

Of course we shouldn't compare a revolver with an M-16 - apologies CenturionMBT - there are just too many other differences besides the barrel length to make a fair comparison.

So let's narrow down the differences to just the barrel length. Let's compare an M-16A2 (21-inch barrel) with a M-4 (16-inch barrel). Both have the same rifling twist (I think). It's a simple conclusion - the M-16A2 wins.

A longer barrel makes the bullet spin through more rifling grooves which steadies the bullet before it leaves the barrel.

But there are other factors. I think that a heavier (ie thicker) barrel offers more accuracy as it is more rigid. Also, I think when making barrels intended for sporting guns and sniping purposes have different forging methods that are normally too expensive for normal assault rifles.

losers.inc SG

whats the fuss? just shoot and kill. Twisted Evil

nismoS132 SG

a closer comparison, and 1 that the saf has, would be m16 vs carbine.

John Ching SG

Hmm! Without trying to sound too technical on the subject, why don't a simple test be conducted on the subject? Neutral

Ooh! There's no need to actually use a rifle for the test since the subject is about the barrel. Just take 2 barrel/ pipes of different length but equal thickness & using equal amount of gas to fire off a projectile at a target of the same distance. The result of the test should be able to give you a rough but clearer ideal as to whether the length of a barrel affects accuracy. Mr. Green

Meia Gisborn SG

If both the 16" and 20" barrels have the same twist rate in the rifling, the projectiles will exit the muzzles with the same spin rates, regardless of barrel length. The projectile's muzzle velocity out of the longer barrel might be a tad higher, but the spin rate (i.e., number of rotations per unit of distance) remains identical to a similar projectile shot out of the shorter barrel.

But there are other factors. I think that a heavier (ie thicker) barrel offers more accuracy as it is more rigid. Also, I think when making barrels intended for sporting guns and sniping purposes have different forging methods that are normally too expensive for normal assault rifles.

In general, heavier, or bull, barrels do a better job of dissipating heat due to the increased surface area on the outside to radiate away the heat. Many competition barrels have flutes or ridges machined along their lengths to further increase the surface area.

Most of the barrels used in civilian AR15-type rifles here in the US are manufactured by the same contractors that supply barrels for the military M16s and M4s using the same materials and methods.

This is an image of one of my AR rifles. It sports a 24" stainless bull barrel with a 1-in-8" twist rate, and is fully capable of sub-1" groups at 100 yards using my competition handloads.

MG

tvdog SG

A heavier barrel is better at handling heat for sustained fire which is why all sustained fire small arms have them. It is better at handling heat, not dissipate heat. During sustained fire when the barrel gets red hot, a thinner barrel would bend - a thicker barrel would not.

But a heavy barrel also adds to accuracy because it is more rigid. That's why they put a heavy barrrel on the AR you pictured - not for dissipating heat. That weapon is meant for very accurate single shots so why would there be any great need to dissipate heat?

And you mentioned that the barrel in that picture is made of stainless steel, that's exactly what I meant when I say that barrels intended for sniping are made with different materials and methods too expensive for military models.

The flutes cut into a heavy barrel is to reduce weight - not to increase surface area for dissipating heat as you claim. And flutes also help add to the rigidity of the barrel.

In older times they add fins onto MG barrels to help dissipate heat for eg the Hotchkiss.

Meia Gisborn SG

Handling heat includes being able to dissipate the heat that is generated. The advantage of the bull barrel is twofold: better heat dissipation and greater resistance to warping from high heat.

But a heavy barrel also adds to accuracy because it is more rigid. That's why they put a heavy barrrel on the AR you pictured - not for dissipating heat. That weapon is meant for very accurate single shots so why would there be any great need to dissipate heat?

The rigidity inherent in a heavy barrel certainly contributes to its accuracy, but the need to dissipate heat still exists. Sustained semi-auto fire, such as is encountered in some stages of "Hipower" shooting competitions, still generates a fair amount of heat (though nowhere that from full-auto discharges!). It takes only a miniscule amount of heat-induced warping to make a competition bull barrel lose its shot-to-shot consistency and accuracy. This may cause target groupings to migrate by only fractions of an inch at 200 yards, but HP competitions have been won and lost by just these amounts.

And you mentioned that the barrel in that picture is made of stainless steel, that's exactly what I meant when I say that barrels intended for sniping are made with different materials and methods too expensive for military models.

Those stainless AR bull barrels are made almost entirely for the civilian market; there is no AR military equivalent.

Current US military specifications for AR barrels call for the chrome lining of the chambers and bores for enhanced barrel life under full-auto fire. Chrome-lined barrels are actually more expensive to manufacture than the non-chrome-lined barrels found on most civilian ARs (the exception being Bushmaster, whose non-stainless barrels are ALL chrome-lined).

The flutes cut into a heavy barrel is to reduce weight - not to increase surface area for dissipating heat as you claim. And flutes also help add to the rigidity of the barrel.

It does both. Read the paragraph describing the purpose of fluting at the bottom of this page at the Bushmaster website.

Interesting discussion! Laughing

MG

baer SG

Greater length means

By extending the calibre length of the barrel from 44 to 55, i.e. by 1.3 metres, a considerably larger portion of the energy occurring in the barrel during firing can be transformed into greater projectile velocity. Greater velocity would translate into a truer flight of the projectile and hence greater accuracy.

see:
http://www.rheinmetall-detec.de/product.php?lang=3&fid=1449

Examples from 'larger guns' better proof than M-4 M-16 comparisons.

Meia Gisborn SG

Better in what way? The scale of the differences, perhaps?

Changes in barrel length affect the ballistics of projectiles fired therefrom, regardless of caliber.

MG

baer SG

155mm guns have moves from 45 calibre to 55 calibre our 155mm being case in point. Other technologies have distorted this simple comparison i.e. extended range base bleed ammo which extend range while keeping same CPI at longer range.

The Base Bleed is a tail unit containing fuel-rich but oxygen deficient materials is screwed to the base of an ERFB projectile. When fired, the unit releases gases into the wake of the projectile via a small port where it burns to increase pressure locally thus reducing base drag. From an L45 barrel a typical ERFB can achieve a range of about 30,000 meters but with -BB can achieve around 39-40,000 meters.

i-SHOT SG

Alright, I got one for you guys.........

We have two AR15/M16 with the same setup and the same barrel length - the only difference is caliber; first is 5.56 and the latter is the 6.5 Grendel.

Accuracy? Effective Distance? etc, etc.... what do you guys think?

Meia Gisborn SG

This website might contain the answers to your questions.

There is an older chap at our club shooting an Alexander Arms "Overmatch" (I think that's what they're called) 6.5 Grendel AR upper with a 24" barrel. I was spotting for him one windless evening recently while he was shooting at the 200-yard range; he was peppering the bullseye and his groups were averaging under two inches at that distance.

Oh yeah, I forgot to mention: his rifle was #@$%&@! LOUD!!! I normally double up on hearing protection (plugs and muffs), but the concussion from his rifle still rattled my skull.

MG

baer SG

calibre length duh not bigger better dah.

larger round longer range better cpi comparison.

5.56mm is too small for comparative as windage affects rounds at that level