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How much psi per shot?

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#1 J51Mustang

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Posted 12 June 2016 - 01:56 PM

Before I get started, I want to make it clear (so that i don't get another warning or banned from the forums ;)) that I AM NOT trying to propose a new idea for a homemade nerf gun. I am trying to do some research before building one and had a question but I can't seem to find an answer through google so here it is:
 
About how much psi is needed to propel a foam bullet around 300 fps? By foam bullet I mean any type of nerd dart (homemade, or stock) that can actually get up to 300 fps without destroying itself while at the same time being accurate and safe. Are there any ways I could calculate how much psi I would need to propel a round of that type at a given fps myself?
 
Any helpful answers will be appreciated. Thanks!

Edited by J51Mustang, 12 June 2016 - 11:47 PM.

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#2 Maniacal Coyote

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Posted 12 June 2016 - 05:44 PM

Stock (elite) darts fly out of control above ~130 fps. (I don't know the exact threshold; I'm just pulling numbers out of my arse.) My guess: 130 fps +/- 5 fps.

For stable flight at the velocities you're interested in, you're going to need stefans, slugs, Artifact darts, or cut-down ACC darts. Maybe trimmed Rave darts would work, too.
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#3 Kilomona

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Posted 12 June 2016 - 06:01 PM

An air blaster will literally tear elite darts apart in the barrel at that speed (trust me, I sacrificed many a dart testing my XBZ) 300 fps for any dart is much to dangerous to use on human beings with a nonlethal intent. I think 120 psi is what alot of people use for about 6-8 good shots, depending on tank size.
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#4 shandsgator8

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Posted 12 June 2016 - 06:12 PM

I'm not engineer or science major, but in addition to the pressure of the air inside an air tank, doesn't the overall air tank size and barrel length play a factor into how fast it can propel a given projectile?

 

Also, can a stock Nerf dart even reach 300 FPS while maintaining any degree of ballistic characteristics?


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#5 DX-Robert

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Posted 12 June 2016 - 09:56 PM

Certain varieties of stock darts *can* remain stable at 300 FPS.  They need to have good weight distribution, well-designed and glued heads, and be "heavy enough".  USCs and ACCs are known stable at that velocity, and do not need to be cut down.  Xplorer V2 darts are stable to at least 260 FPS and should be to 300.  FVJs and FVNs/VTNs are somewhat stable, you can have a war with them out of DIY level blasters, just not with the usual accuracy.

As far as I know of, you need around 40-50 PSI to achieve 300 FPS, but I've never attached a gauge and thus don't have a concrete answer.  Note that the dart fit plays a large role in how much velocity you can milk out of a tank.  Bad dart fit will reduce your velocity by as much as 80 FPS or even more.  Also, what you think is a good fit probably isn't - if you don't test all your options, you may be left getting less velocity than the tank is actually capable of producing without ever realizing it.  And, of course, lighter darts will generally achieve higher velocity, but may not be as stable as heavier darts.

TL/DR:  This isn't something you can just calculate.  You need to do real testing.


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