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Barrel Length

Finding the right length

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#1 pat 1st Lt

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Posted 13 April 2006 - 05:06 PM

Dear Forumgoer,


Recently I've been experimenting with different barrel lengths for my UBS system stolen from Baghead, from the here and here

(I hope I did that "tag" thing right. Sorry if it's all messed up and just a bunch of URLs)


Anyway, I've been experimenting with different length barrels, made of the same materials from the same shipment of material, and using the same darts, just so I get fairly accurate results. While I was cutting away at my PETG and Brass, I wondered "How do other people determine their barrel length so effectivley? It seems like in all the 'write-ups' you find, there's always the little thing that say 'I've found 8 inches of brass to be best', or something."


So, that's what I'm here to ask: how do you know that the length of your barrel you've got on now is giving you maximum performance?


Do you just cut it long, and then keep hacking away, an inch at a time between range testings?

Do you just guess and hope?

Do you wait for 'them' to do the research for you, and then copy it?

Do you use some super-secret equation, or calculations?

Do you have voices in your head that secretly whisper to you while you sleep what barrel length to use?



I'd like to know, and I'm sure there are many others out there that would too.


So, when you reply, just say Spring Guns: ' insert whatever you do to find it', Pump Guns: 'insert whatever you do to find it'.


Thanks in advance guys. I know there'll be some secret ancient Nerf technique revealed to us by the old members for determing the best barrel length. I can feel it.




Sincereley,
Pat
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#2 GeneralPrimevil

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Posted 13 April 2006 - 05:12 PM

I didn't really read much of that post...I use equations (x=?) and a computer program (GGDT, not really what it was originally designed for). Unfortunatly the program involves a lot of other guesswork...

That and I have a little voice in my head...when it says 'kill' I ignore it, for the most part, but when it says 'twelve inches' I listen...it occasionally says 'burn' , which I do at the appropriate place and time...
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#3 Vicious-V

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Posted 13 April 2006 - 05:12 PM

Pump Guns: 4-5X air tank length
Spring Guns: Length of plunger tube.

Edited by Vicious-V, 13 April 2006 - 05:13 PM.

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#4 Flaming Hilt

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Posted 13 April 2006 - 05:30 PM

I use a quarter of the volume of air I'm using.

For example, go here, type in the active length of your plunger and the diameter or radius. Hit "Diameter" or "Radius," respectively. Note that number. Then go back and put in the diameter or radius of your barrel, and guess and check the length 'till you get the same answer for volume. Divide by four.

For pump guns, just take the volume of the pump shaft times the number of times you plan on pumping it. Use the same calculator until you get that volume for your barrel, divide by four.

NOTE: FAILURE TO DIVIDE BY FOUR MAY RESULT IN EXCESSIVE BARREL LENGTHS (say, 12" on a NF).
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#5 davidbowie

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Posted 13 April 2006 - 06:03 PM

Pump Guns: 4-5X air tank length
Spring Guns: Length of plunger tube.


Do you actually do this? You must have some pretty kooky guns, then. You forgot to account for diameter.

The best ratio (according to bolt) for a spring gun is about 4:1 C:B.

For air guns, it's debatable, but around 1:1 should be good.
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#6 m15399

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Posted 13 April 2006 - 06:32 PM

I say:

Depends on friction in barrel
Depends on seal in barrel
Depends on plunger seal (spring)
Depends on valve open speed (air)
Depends on power of spring (spring)
Depends on ID of valve/barrel (air)

My advice:
Start with a really big barrel. Measure range. Cut it off in ~4-6" sections, measuring at each length. When the range starts to go down instead of up, do a few more measurements then stop. If you plot all the points on a grid (barrel length to range) you will see that it makes a curve. The peak of this curve is the barrel length you should use.
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#7 Maverick Master

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Posted 13 April 2006 - 08:37 PM

Spring guns- So the dart is leaving the barrel as the plunger is at the end of the
plunger tube. The equation is right here.
Just scroll up to the barrel section.

Edited by Maverick Master, 13 April 2006 - 08:45 PM.

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#8 Dr Nerf

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Posted 14 April 2006 - 10:54 AM

Look at what my search turned up:
http://nerfhaven.com...?showtopic=4618

It seems that there are two ways to find the true "ideal" barrel length for range.

The empirical method is the eaiser of the two. Basically, you try out a bunch of barrel lengths and find the range that each other gets. The barrel length is the independent variable (x), and the range in the dependent variable (y). Use a graphing calculator to find a quadratic regression to represent these points. Then, use the equation (-b/2a) to find the vertex, or maximum point. This equation would yield the x value (barrel length) that would result in the highest range.

The second method is genius and requires physics knowledge. I am basically going to try to outline what merlinski said. You have to try to find the point at which the dart has no acceleration (a=0) (stops accelerating). After this point, the force of friction on the dart causes the velocity of the dart to decrease. Before this point, the dart is accelerating and building velocity. To get the highest range, you want the dart to have the highest possible velocity when leaving the barrel. Essentially, you are trying to find the distance the dart has traveled when the force of propulsion equals the force of friction on the dart. The distance that the dart has traveled when the velocity is maximized is the ideal barrel length.

Using calculus, you know that a function could have a maximum or minimum when the derivative (rate of change) of the function is equal to 0. You want the velocity to be maximized when the dart exits the barrel. The derivative of velocity is acceleration, so you can see again that you have to find the distance traveled when the acceleration of the dart is equal to 0.

To do the second method, you would need to find out the force of propulsion that the dart experiences. I don't really know how to do that, but I have some guesses. For spring guns, I am pretty sure that it is related to the force of a spring equation (F=kx I believe), but I don't have a clue about this for air pressure guns.

EDIT:

The second method also assumes that the seal in the barrel is perfect so that all of the force of propulsion goes into the dart. The valve that is used or the seal on the plunger are not in the method but they are still important. If the valve does not open fast enough, much of the force will not initially be exerted on the dart. The same goes with the seal of the plunger in a spring gun. If the seal is not perfect, some of the force will be lost. So, the force of propulsion should be different if the valve is not opened fast enough or the seal is not perfect.

Edited by Dr. Nerf, 14 April 2006 - 01:13 PM.

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#9 GeneralPrimevil

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Posted 14 April 2006 - 01:40 PM

Air pressure guns should be something to the effect of S.A. of the rear of a dart times the pressure of the compressed air within the valve body, would it not?

I dunno, it makes sense and is what I use for air cannon and other things...

It also pulls off of the whole theory behind the melted cone in the back of a dart: harder surface (heat-treated FBR -vs- regular FBR) with more area (L.A. of a cone -vs- area of a circle) for the air to hit, resulting in an increased amount of force hitting the dart.

[hijack]

Holes/melted cones in the backs of darts make them a bit harder to use, although make the dart fit the barrel better and allow more S.A. for the air to hit. So why not make a boat-tail instead if one has a tight-fitting barrel/FBR? That way, the dart is still durable, but S.A. is increased, resulting in increased force behind the dart, meaning faster acceleration (resuting in the need for a shorter barrel length) or a higher M.V. (with the same barrel length). Now time to try and figure out how to get a sharper point without using a hard substance, yet still is capable of minimizing drag...perhaps something to the effect of a sculpted length of FBR bonded to the front of the dart? I dunno, but seriously, enough gun work. Look into the projectile for more range now...

[/hijack]

If someone really wanted to be special, they could remove the air in their barrel, pumping it into the firing valve/reservior/chamber, resulting in less weight of the projectile, and more distance due to faster acceleration and a higher M.V. I just don't know what could be used as a burst disk at the muzzle so as to achieve a vacuum...
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#10 Doom

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Posted 14 April 2006 - 03:40 PM

In the situation you described, the weight loss of the dart would be negligible, as well as any pressure increase in the pressure chamber. Regardless, heavier objects have more momentum and because of that typically better distance. That is why you weigh your darts. Anyway, if there is space for a vacuum to be created, the dart will only move back further in the barrel.

A better idea would be to pump once more and to weigh the darts better.
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#11 I Luv Painful Mods

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Posted 14 April 2006 - 04:06 PM

I have a little voice in my head...when it says 'kill' I ignore it, for the most part, but when it says 'twelve inches' I listen...it occasionally says 'burn' , which I do at the appropriate place and time...

Hahahaha, That made me laugh so hard!

Well anyway i have no idea watsoever i just make mine look cool.

Sometimes like when you want to cause max pain when shooting
your really annoying sibling, than that can be good to know.
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#12 Talio

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Posted 14 April 2006 - 04:27 PM

I have a little voice in my head...when it says 'kill' I ignore it, for the most part, but when it says 'twelve inches' I listen...it occasionally says 'burn' , which I do at the appropriate place and time...

Hahahaha, That made me laugh so hard!

Well anyway i have no idea watsoever i just make mine look cool.

Sometimes like when you want to cause max pain when shooting
your really annoying sibling, than that can be good to know.

Follow the COC and fix your god damn shift key.
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#13 VeggieBoy 3000

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Posted 14 April 2006 - 05:51 PM

I normally look into my big bin of assorted nerf crap, and see if what kind of barrels i have lying around. If the gun is a 'long range' gun I normally find one that looks a bit longer. If its a smaller spring pistol I'll look for a smaller barrel.

Truth be told, I dont think that finding the exact best length is worth the time, whether it is spent testing or figuring equations. Just use intuition and go with what looks best. The extra 5 feet of range isn't gonna make much difference, trust me.

Once you've been doing it for long enough you really can just eyeball what's gonna be best for your particular mod.
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#14 cxwq

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Posted 15 April 2006 - 10:17 PM

Do you wait for 'them' to do the research for you, and then copy it?

That is precisely what the majority of people do, whether they admit it or not.

I started off with the empirical method, testing several lengths until I found the optimal barrel for each gun. After a while I got a feeling for what to use based on what I'd done in the past that was similar.
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#15 pat 1st Lt

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Posted 16 April 2006 - 04:50 PM

Do you wait for 'them' to do the research for you, and then copy it?

That is precisely what the majority of people do, whether they admit it or not.

I started off with the empirical method, testing several lengths until I found the optimal barrel for each gun. After a while I got a feeling for what to use based on what I'd done in the past that was similar.

My problem with this cutting the barrel method is this: let's say you have an eight inch barrel. You know eight inches is too long, you you cut it to seven, and the range improves. You cut it to six, and the range improves.

Now, how do you know whether cutting it to five will improve, or unimprove your ranges? If you cut it to five and it improves, good for you. If you cut it to five and the dart starts to fish-tail, you have to take the gun apart, unatttach the barrel, and put another 6 inch one on.

That's my problem: I don't want to re-do the mod a lot and start ruining the structural integrity of the gun.

That's why I've opted to steal baghead's UBS, because you can have a 6 inch barrel, and easily swap it out and try a 12 inch barrel. But, finding an interchangable barrel that works decently well on many high-power guns is difficult.

Trying to find the optimal barrel length for a Crossbow, then finding the optimal for a Lanard Blast Bazooka, the for an AT3K, then an AT2K, then finding it for a Splitfire, and then for a Secret Shot Two is difficult to do.

Even more difficult is to then try to find the 'average' (For lack of a better word) barrel length that works well on ALL of these guns.

After a lot of testing, I've decided to go with 8 inch barrels. 8 inches is too long for some guns (Splitfire) and too short for some (LBB, Crossbow), but works decently well for all. None of the guns are working to 'full' potential, but they are getting very decent results given the ROF increase.


However, since these are removable barrels, I could just make some 11 inch ones for the Crossbow, some 14 inch for the LBB, some 6 inch for the Splitfire, and some 8 inch for the SS2. But, the point of this little experiment was to find a Universal Barrel, that could be used on all our high-power primaries and secondaries. I feel I succeeded in this project, as I did what I set out to do, even if it isn't getting the range results I hoped for.



On another note, cxwq, I agree with you that the majority of people simply wait for someone else to buy three or four guns, mess around, and do some testing. While this is 'safer' in the sense you will much less likely ruin the gun, but it is sort of weasle-y to do. It's not really immoral, but it lacks creativity, and is not in any way fun (Which is why I mod).



Wow... I've typed too much. I'll just hit 'submit' and shut up.


Sincereley,
Pat
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#16 Pineapple

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Posted 17 April 2006 - 10:14 AM

Actually, Pat, you were answering your own question, and in a way that is in agreement with cxwq, in whom I agree with his methodology.

In my opinion, barrel length is dependent on so many factors, one of which is the brand and type of FBR used for stefans, and even brand and types of PVC and CPVC. Brass and PETG seem to be more consistent, though I only have one type of PETG, so I may be wrong there too. One man's "perfect" will suck in another man's blaster barrel; again my opinion. There's some fairly close margins where homemade ammo is primarily universally effective in several blasters, and the range variations will probably be negligible.

I will sometimes go through 4-6 feet of PVC to optimize barrel length, and the extra lengths of pipes actually can be used as test barrel material. I'm also a fan of the hot glue gun when it comes to barrel mods. Once the ideal is found, the hotglue comes off and the 2 part epoxy goes on.

My problem with this cutting the barrel method is this: let's say you have an eight inch barrel. You know eight inches is too long, you you cut it to seven, and the range improves. You cut it to six, and the range improves.

Now, how do you know whether cutting it to five will improve, or unimprove your ranges? If you cut it to five and it improves, good for you. If you cut it to five and the dart starts to fish-tail, you have to take the gun apart, unatttach the barrel, and put another 6 inch one on.


I know. Fun, huh?

I actually have fun doing that, modifying and tweaking and working to get the best all-around performance out of our blasters.

That's my problem: I don't want to re-do the mod a lot and start ruining the structural integrity of the gun.


I don't know...I don't see any problem with structural integrity; perhaps since I usually modify with assembly and disassembly in mind. I don't glue up everything in sight...I'm not saying you do, but I've seen some modifications that definitely look "one-way".


None of the guns are working to 'full' potential, but they are getting very decent results given the ROF increase....

...But, the point of this little experiment was to find a Universal Barrel, that could be used on all our high-power primaries and secondaries. I feel I succeeded in this project, as I did what I set out to do, even if it isn't getting the range results I hoped for.


I agree there.

What intrigues me sometimes is how everyone wants their blasters to be absolutely the maximum range possible at any expense, then they post about how it broke soon afterward.

The way we Nerf, even a mod that gets 30 feet or so is successful, since we're always on the move and closing in and dodging stuff. I use short (by comparison) barrels on my AT2k, because I don't shoot it from 80 - 90 feet away all the time...I'm usually within 25 - 30 feet when we're shootin' it out.

I'll take modest range and durability over a maxed-out blaster that's ready to fail, anyday.



-Piney-
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#17 pat 1st Lt

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Posted 18 April 2006 - 09:21 AM

I'll take modest range and durability over a maxed-out blaster that's ready to fail, anyday.

-Piney-



Here here. Too many people like to band their guns, put in over-powered springs, try to expand air tanks by drilling them out and adding vinyl tubes. It's ridiculous.


And yes, I agree on your point about different brands, dart thickness, etc.

I never set out to find the one-and-for-all best barrel. I set out to discover what other people do to find the 'best' barrel for themselves.



Sincereley,
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