Barrel length Questions.

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JDShapp

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Jun 7, 2015
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Indiana, United States
As I look over my bullpup options for the future I've started to wonder just how much length will change potential accuracy and power. Originally I was all but set on a Vulcan, Wildcat, or Priest(if it's good). Then my father told me to forget about the ergonomics and look at the numbers. That's when I noticed the barrel length differences of the 3.

So is 2 inches in barrel length going to make much of a difference?
 
Barrel length doesnt effect accuracy with all else being equal. unless you plan on using open sights. The length does effect power or potential power and how efficient it will use air. How efficient a given length is also depends on the tune and valve set up. I think its common for airguns to lose or gain 10 - 15 fps per inch of barrel length. So not a huge difference but again the rifles set up and valving will play a part in how much is gained or loss.
 
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Gentlemen,
barrel lenght does does make difference:

- longer barrel is more efficient, thus able to give more power, or more shots per fill
- longer barrel is more efficient, so less noise
- from technical point, accuracy-wise, a longer barrel is NOT more accurate. In practical reality, shooters may find short barrel more accurate as the pellet is shorter time in the barrel, so less time for the shooter to screw up the shot

First two reasons are the main reasons why bullpups make sense in airguns...

Regards, Mike
 
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I've done a little research on this topic and there is certainly no concencus. 

There good reasons for both sides of it. Here are some as I understand them:

longer barrels produce more power which delivers a flatter trajectory which will help some shooters to be more accurate. A faster pellet will also have less time to be impacted by the wind.

longer barrels are heavier. Extra weight at the front provides more stability which helps with accuracy. Target rifles are made heavy for a reason

I have read some credible sounding opinions that state that it is more about finding the right barrel length for the energy produced. I.e. Too much energy down a shorter barrel produces more turbulence but a shorter barrel with an appropriate pellet speed can be just as accurate as a longer one.

My personal experience has been that it is easier to shoot my longer heavier bullpups well and harder to hold the short lighter ones steady. 
 
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Length as an indicator of accuracy is snake oil. However in the AG application and somewhat also in the firearm application, it's hard to produce high muzzle velocities with short barrels being that the projectile spend less time inside the barrel being pushed by expanding gasses or air pressure.
So the trick is to have a short and stiff barrel as possible for the power/velocity needs. This ensures two things when it comes to accuracy. #1. time spent inside the barrel and hence subject to any movement/shift by the shooter or shot cylce mechanics. #2. A short barrel is going to be stiffer than a longer one with the same OD, which is suboptimal to accuracy. The last obstacle can be fixed with barrel tuners, but is a PIA. 
Overall weight of the barrel has little to do with anything, all tough overall weight of the whole gun does have an impact. What I mean is, if you had a long heavy barrel on a flimsy lightweight chassies, you would reap no benefit in the accuracy dept. If you had a heavy chassies, with a shorter lighter barrel, you would reap benefits. As the platform you are shooting from has more inertia that resists movement. 
So as a conclusion, go as short/stiff/thick as you can on the barrel while keeping velocity where you want it.
 
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If the weight of the barrel has nothing to with anything, then why do barrel makers offer heavier and lighter barrel options? The answer is because the weight of the barrel does have something to do with something. Just to preempt the old "that's a powder burner thing" response. LW offer multiple barrel weight and thickness options specifically for air guns and Daystate offers a heavy target barrel option for it's rifles. 

Adding weight at the back does not necessarily achieve the same things as weight at the front. Balance is important for accuracy. At stores that sell accessories for high end target rifles, one of the things they offer is barrel weights.

Also, people that know lots more than me about this stuff are always going on about harmonics and vibration which most definitely is effected by weight and thickness. 

 
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Zebra,

When manufacturers are using thicker barrels to increase accuracy of their rifles, it's not to add weight, that is a by product of what they are doing. They are adding stiffness (modulus) to their barrel. As you correctly surmise, it's about harmonics, and you can only combat harmonics in a few ways, adding thickness to increase stiffness is the cheapest and easiest way to do this, but the drawback is weight increase in the wrong end of the gun. I cannot think of any gun where you do not want the center of the mass close to your body, much easier to control.
The other solutions to increase barrel stiffness and/or accuracy are both time consuming and a bit of trial and error. One solution is sleeving the barrel in stiff materials like carbon fiber, which also have the benefit of being a different modulus, which harmonics do not want to propagate trough (going from one density to another) Tuning the barrel with a tuning device (small weight) this is time consuming and a round specific solution. Tensioning the barrel is another effective method of controlling harmonics as well as add overall stiffness. 
The primary accuracy issue we are talking about here is harmonics, or waves causing nodes and anti nodes to form along the entire length of the barrel, and you cannot get rid of it completely. Only thing you can do is to minimize it, and/or force the nodes to form where you want them too.
 
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"Windmeister"Zebra,

When manufacturers are using thicker barrels to increase accuracy of their rifles, it's not to add weight, that is a by product of what they are doing. They are adding stiffness (modulus) to their barrel. As you correctly surmise, it's about harmonics, and you can only combat harmonics in a few ways, adding thickness to increase stiffness is the cheapest and easiest way to do this, but the drawback is weight increase in the wrong end of the gun. I cannot think of any gun where you do not want the center of the mass close to your body, much easier to control.
The other solutions to increase barrel stiffness and/or accuracy are both time consuming and a bit of trial and error. One solution is sleeving the barrel in stiff materials like carbon fiber, which also have the benefit of being a different modulus, which harmonics do not want to propagate trough (going from one density to another) Tuning the barrel with a tuning device (small weight) this is time consuming and a round specific solution. Tensioning the barrel is another effective method of controlling harmonics as well as add overall stiffness. 
The primary accuracy issue we are talking about here is harmonics, or waves causing nodes and anti nodes to form along the entire length of the barrel, and you cannot get rid of it completely. Only thing you can do is to minimize it, and/or force the nodes to form where you want them too.
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For all of my rifles, I like the balance to be in the center and close to my body as you say but I am mainly a hunter. If I was making a target gun for BR, I would specifically look for a heavy barrel to keep it weighted down up front. The more weight on the front rest, bipod or bags, the better for holding it steady. Some bipods attach directly to the barrel...

For any heavy gun, i wouldn't want all the weight at the back with a lightweight barrel up front. I would want it to be properly balanced. For any scenario where I was not shooting from a bench, rest or sticks, I find it hard to hold a rifle straight if it isn't balanced right, if it's heavy at the back, I would want a heavy barrel and if the rifle was light overall, I wouldn't want a heavy barrel making it "front heavy". 

If I needed to use a target gun for multiple disciplines, I would want shooting weights to shift the balance for different positions. In general, I like front heavy for bench rest shooting though. 

Haven't you ever experienced a gun that is hard to hold steady because it's so light and short?
 
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The question was about accuracy.

Handling and weight distribution is the easiest thing to fix if your rifle is rear heavy. Besides I cannot on top of my head recall any rifle that I have shot that was hard to control due to being rear heavy.
I also think, in general, that if that was a huge issue the idea behind a bullpup would be dead on arrival.
I do agree that balance is important. But I am pretty sure most if not all manufacturers pick their barrels based on accuracy for the application. Weight is not a wanted "need" but a result of trying to have as much stifness as possible. On many centerfire high accuracy barrels you see them cut grooves along the lenght of the barrel, for two reasons, weight saving, and heat dissipation.
AG dont need heat dissipation, so you could probably cut pretty deep outside grooves on a pretty thick barrel to improve stifness. And it would look cool as heck.
 
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"Windmeister"The question was about accuracy.

Handling and weight distribution is the easiest thing to fix if your rifle is rear heavy. Besides I cannot on top of my head recall any rifle that I have shot that was hard to control due to being rear heavy.
I also think, in general, that if that was a huge issue the idea behind a bullpup would be dead on arrival.
I do agree that balance is important. But I am pretty sure most if not all manufacturers pick their barrels based on accuracy for the application. Weight is not a wanted "need" but a result of trying to have as much stifness as possible. On many centerfire high accuracy barrels you see them cut grooves along the lenght of the barrel, for two reasons, weight saving, and heat dissipation.
AG dont need heat dissipation, so you could probably cut pretty deep outside grooves on a pretty thick barrel to improve stifness. And it would look cool as heck.



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+1
Stiffness and heat dissipation are the two reasons for thick barrels. Fluting as stated by windmeister increases the surface area to dissipate heat faster and adds stiffness. Airguns only benefit from a stiffer barrel and have no need for heat dissipation. Weight of a rifle is a personal choice and for me a lightweight rifle that is well balanced works as well as a heavier well balanced rifle for accuracy.
 
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