fps and range calculator formula

Discussion in 'General Accessory Discussion' started by ArielNechemia, Jan 4, 2013.

  1. ArielNechemia

    ArielNechemia New Member

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  2. Knief

    Knief Moderator Moderator

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    Sure thing. You have three variables, feet per second (FPS), bb mass (m), and muzzle energy (E). You need two to determine the third, and typically you want to use your FPS at a specific weight to determine your gun's muzzle energy. Then, you use that muzzle energy (because it doesn't change unless you upgrade your gun*) to determine what the FPS would be with a heavier or lighter bb. Here's the equation to do it.

    FPS= √(2000E/m)/(.3048)

    Units
    -FPS is in feet/second (duh)
    -bb mass in in grams
    -Muzzle energy is in Joules (the most common measure we use)

    Remember, don't take the square root of the .3048 term. The equation isn't entirely clear about that as written because writing equations in a text box is difficult. Your easiest option here instead of working out every possibility by hand is to make an excel spreadsheet that allows you to insert values for two of the three variables and have it chuck out the third.

    Trying to calculate range is something of a joke in airsoft. Two guns shooting the exact same FPS with the exact same bbs can have completely different ranges based on hop up and barrel tuning and quality. There's really no way to take these things into account in a simple equation, and you'd have to have a pretty thorough understanding of fluid dynamics to even begin to try. You're better off just asking people with similar set ups what kind of range they get.

    *This isn't entirely true. Cylinder volume vs. barrel volume, air loss, and other factors effect how your gun reacts to a change in bb mass. Most guns actually gain just a bit of muzzle energy when you use heavier bbs. It's negligible enough on most guns that we don't take account of it when we chrono them, but it does exist and it's important to know about.
     

  3. ArielNechemia

    ArielNechemia New Member

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    awesome, thanks i really appreciate it.
     
  4. Lefse

    Lefse Well-Known Member Supporting Member

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    Yeah, the range numbers I got from that calculator are waaay off. I plotted in the specs of my MP5K, shooting 1J, and got only 130 feet range with .25's, while in reality it's closer to 180 feet. Knief is right, calculating the effective range of an airsoft gun is almost impossible, there are just too many variables. The equation would probably look like some alien language hehe.
     
  5. ArielNechemia

    ArielNechemia New Member

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    so pretty much the only way to find out the range is to just shoot and count?
     
  6. Knief

    Knief Moderator Moderator

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    That or shoot and make a friend count. But yeah, there's no way to use math to figure out your range because the number of factors that effect your range are great and incalculable. Two guns that have near identical set ups may have very different range if one gun has had a few extra tuning steps performed on it. There's no equation that can take that into account. You could do some statistical analysis to come up with an approximation if you knew all of the variables to test and then tested them. That would take resources that very few have and even fewer have reason to use. It's just easier to shoot and pace it out.
     
  7. brokenarrow

    brokenarrow Well-Known Member

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    I just use an Airsoft calculator on my phone :cool:
    I no good math ;)
     
  8. L5132

    L5132 Active Member

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    Did you look at any of the other posts? No calculator cannot give accurate results for range.
     
  9. brokenarrow

    brokenarrow Well-Known Member

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    Well, sorry, I loath math, even if its for something I like, I don't need accurate results, just close enough
     
  10. L5132

    L5132 Active Member

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    Still haven't read any of the other posts. Regardless of whether or not you like math, the only thing you can calculate is FPS, which while related to range, is not the only factor in range. The hop-up has a much larger effect on range. If your gun shoots 700 FPS with no hop-up, it will be easily be outranged by guns with much lower FPS and a hop-up.
     
  11. brokenarrow

    brokenarrow Well-Known Member

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    -____- don't think I know this? I understand that FPS is not directly related to range, I'm just saying that I have a calculator on my phone which takes FPS and BB weight and pops out a rough range estimate, and I have read this entire thread before posting, just saying there's an app for that (joke) so don't hate me
     
  12. L5132

    L5132 Active Member

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    *sigh* What you aren't understanding is that the range can easily be off by as much or more than 1/3 of the claimed range, which is a huge inaccuracy.
     
  13. brokenarrow

    brokenarrow Well-Known Member

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    Ok, I won't use it anymore, forget I ever mentioned it