Accuracy Affected By Length?

13485 Views 18 Replies 9 Participants Last post by superman365, Dec 29, 2012

jtilley

Discussion Starter · Dec 26, 2012

How much is our accuracy improved by a longer barrel? I shot two 9 shot groups first with 5'gun then with a 3'6" gun. Both were constructed of 1/2" pvc and I used the same darts in both groups. As you can see in the pics the 5'gun was far more accurate, not to mention how much harder it shoots

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NightKnight

· #2 · Dec 26, 2012

OK, you have my curiosity now....

Were the barrel exits the same distance from the target?
What was the range?
Were the barrels fixed to something during the test?

Carbon

· #3 · Dec 26, 2012

I shoot a 3' 2" blowgun with very consistent accuracy. I think identical darts is the key to accuracy, not barrel length. But I am curious to see how this pans out...

The Warrior

· #4 · Dec 26, 2012

I'm very curious about the range myself. If it was at a fairly close range, I wouldn't expect much difference. Longer ranges, definitely.

Carbon

· #5 · Dec 26, 2012

Also, when shooting a longer BG, the barrel gives you more or a "line" to aim with. So if you aim by putting the target between the two "ghost" ends of the barrel, the longer one has a smaller space between the two ends and therefor a more precise shot. Just a thought...

treefork

· #6 · Dec 27, 2012 (Edited by Moderator)

I use a 7 ft piece of electrical conduit.The power and range is quite noticeable. I go one step further and drill symetricaly placed holes to vent in the last inch of the bore . Reduces turbulance as the dart is exiting and the dart is off to a more stable flight after leaving the bore.

Lightgeoduck

· #7 · Dec 27, 2012 (Edited by Moderator)

I would imagine barrel length for blowguns are comparable to barrel length with firearms. The longer the barrel the farther the distance the accuracy remains. So, If you keep everything consistent, the shorter barrel will lose accuracy first as you increase the distance from the target.

Loosely speaking, of course

LGD

jtilley

Discussion Starter · #8 · Dec 27, 2012 (Edited by Moderator)

In the above pics I was seated 20' from the target resting the gun on my knees. After reading the comments I decided to try again. This time I was seated 35 'from the target with the guns resting on a cushioned bar stool. I also used my shortest gun 3'2" against the 5' gun, Besides the tighter group the 5 'gun was easier to shoot. Also, I aimed at the x with the long gun, but with the short gun I had to hold over the box. I am sure their are lots of variables to consider (such as my lungs, lol ) therefore these groups can only be used as a starting point. I am interested in putting together ideas on how to have a more foolproof test of this theory such as constant/controled air. Solid mounted gun, etc. I look forward to your input.

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Carbon

· #9 · Dec 27, 2012

I'm thinking something like an air cannon

but pumped up only 1-2psi

jtilley

Discussion Starter · #10 · Dec 27, 2012

Carbon said:
I'm thinking something like an air cannon but pumped up only 1-2psi

My thoughts exactly, although I was unsure of the air pressure. I do have an air cannon that I made sometime back. I may see if I can modify it to try the different length barrels.

NaturalFork

· #11 · Dec 27, 2012

Longer is generally more accurate. From my own personal shooting.

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orcrender

· #12 · Dec 27, 2012

I think the longer tubes are more accurate. I am with another member that it gives you a better aim at the target, but also the increase in speed produces less drop. My 5' copper pipe beats out its 4' brother at the same range.

NightKnight

· #13 · Dec 27, 2012 (Edited by Moderator)

FYI - In firearms, barrel length does not actually affect accuracy in and of itself. It is indeed a widely held myth though. A longer firearm barrel can/will increase velocity, which at a distance will decrease range drop, and wind deflection will have a reduced effect on accuracy. Also, a longer "rifled" barrel will allow for a more stable spin on a bullet helping with accuracy. Two bullets exiting two identical smooth bore barrels at the same FPS, with one barrel being 1' and the other 5', will have the same accuracy. Make those barrels rifled, and the accuracy will be greater with the 5'. Or, using a large cartridge with plenty of gunpower, the the 5' will be more accurate because the bullet will have a higher velocity.

My current theory is that a 5' blowgun has the same accuracy as a 3', assuming that the darts are leaving at the same speed. I have this theory because (I believe) the accuracy of the dart is more driven by the aerodynamics of the dart (cone shape), once it leaves the barrel, than the accelerated mass of the dart itself over a given distance it travels in the barrel. I would love to have someone prove me wrong though!

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NightKnight

· #14 · Dec 27, 2012

NightKnight said:
is more driven by the aerodynamics of the dart (cone shape), once it leaves the barrel

A little more clarification on my opinion on this, as it relates to aerodynamics. I believe that dart accuracy is most affected (in cone-tail style darts) by:

1. The drag generated via laminar boundary layer airflow across the entire surface of the cone, and the drag forces that it applies consistently across the horizontal and vertical axis(s) of the dart.
2. By the turbulence generated in the low pressure area behind the cone, and the drag is creates. This drag is also applied in a consistent fashion because the cone is round, so that there is not a greater pull either in the vertical or horizontal direction.

NightKnight

· #15 · Dec 27, 2012

Here is an image of a cone in flight. This will hopefully explain what I am getting at. The lower the speed, the less pressure the boundary layer applies to the dart keeping it going "straight". With lower speed the low pressure zone asserts less of a force on the dart. Also, lower speed would mean that the turbulent zone would be closer behind the cone, potentially causing deflection.

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jtilley

Discussion Starter · #16 · Dec 27, 2012

Very good points Knight, however, with the same amount of air pressure the longer barrel will produce more velocity causing the boundry layer to apply more pressure to the cone , therefore the dart from the longer gun would be more accurate. Just my thoughts, I am interested in how this will turn out

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NightKnight

· #17 · Dec 27, 2012 (Edited by Moderator)

jtilley said:
with the same amount of air pressure the longer barrel will produce more velocity causing the boundry layer to apply more pressure to the cone , therefore the dart from the longer gun would be more accurate.

Yep, I imagine that you are correct!

NaturalFork

· #18 · Dec 27, 2012

With a longer pipe it means the pipe is heavier and less susceptible to movement. Kind of like the long stabilizers on an Olympic recurve bow. I think that is in part why they are more accurate for me.

superman365

· #19 · Dec 29, 2012

I have always found that longer barrels give me more power, accuracy, and distance

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