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Easy way to figure FPS

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Easy way to figure FPS

Unread postAuthor: Extrusion » Thu Oct 12, 2006 12:59 pm

I recently went to a site that showed how you could figure fps with 2 peices of paper and 2 microphones well i didnt have a microphone so i can up with this im not 100% sure how acurate it is but i should give you a rough number.

Ok if you dont have a microphone recored you shooting something like a peice of wood from a number of feet back like 10' should be good now put the video on your computer and download Audacity just google search for it its free now open the video in Audacity and it should show you the sound pattern.

Now play it and stop at the point you hear your gun fire.

Once you have stopped at the point your gun fired zoom in on it and find how many milliseconds it took for the projectile to hit the target.

You should get something like 33 milliseconds (.033 seconds; devide milliseconds by 1000 to get seconds) but it all depends on your gun.

ok now for the easy math (Feet Divided by seconds Equals Ft/s)

so it would be 10/.033=303.03030... wich rounds to 303 feet per second.

if you shot from five feet you would do 5/.033 and so on.

Sorry i couldnt get to many pictures but its pretty easy to understand if you need any help post here or pm me.

P.S. If Audacity opens the video file but the sound is a fcked up youl have to find a way to rip the sound from the video, but my cameras videos came out as MPEG's and it opened them fine.
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Unread postAuthor: jrrdw » Thu Oct 12, 2006 4:21 pm

I think theres a easier way, measure from the end of your barrel to the target, get a friend to time the shot, how ever much time it took the ammo to hit the target, is how many feet per second. Pretty easy, huh.
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Unread postAuthor: saladtossser » Thu Oct 12, 2006 5:27 pm

there was this one thing about hang time though, you measure it and work with the gravity acceleration constant
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Unread postAuthor: djt » Thu Oct 12, 2006 6:44 pm

jrrdw that wont be accurate at all unless your target is like a couple hundred feet away. not many people have that much space and it might be hard to hit the target.
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Unread postAuthor: jrrdw » Thu Oct 12, 2006 7:20 pm

I bet if i could'nt hit it the 1st time, i get it the second shot. Just a question-where do you guys shoot at if you don't have at least 100 yards? Ya know? and please don't say mini's.
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Unread postAuthor: saladtossser » Thu Oct 12, 2006 7:31 pm

no offense, but i got more than that and i still wouldnt use your idea
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Unread postAuthor: Extrusion » Thu Oct 12, 2006 8:02 pm

well at 10 feet it takes only milliseconds to hit a target...your friend better have some damn good reflexes lol but anyway this does work very well my bb gun shoots around 700 fps i knew that already i tyried using my method and got exactly 689.3 fps =p
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Unread postAuthor: jrrdw » Fri Oct 13, 2006 7:10 am

Both ways take alot of steps to complete, but my idea gives you some excersize, lol!

OFF TOPIC- When i was in rehab from my car wreck, i met a retired cop who told me if your driveing 50mph your traveling 82 fps.

FORMULA- Speed of travel + half + 7

Simple math, easy enough.

I think there should be a easier way that can be done without alot of equipment, be able to do it on the spot.
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Unread postAuthor: boilingleadbath » Fri Oct 13, 2006 2:56 pm

...50 mph is 73 mph, and 0 MPH is NOT 7 fps.
Now, for highway speeds, "fps = 1.5MPH - 3" would work fairly well. It's only acctualy correct for one speed (1.466mph = 1.5MPH - 3 [solve for MPH]), but it's "close enough" for a limmited range.

That said, it's best to do these sorts of measurments over short ranges; over longer ranges, air drag significantly decreases the average speed, which would interfere with the measurment of what we are typicaly interested in: muzzle speed.

It might be more useful for elevation loss calculations, though.

Anyway, something the OP didn't point out: you have to adjust for the time it takes the sound of the projectile impact to travel back to you.

This will either involve trig', a tape-measure, or merely placing the recording device 1/2 way between the target and the muzzle.
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Unread postAuthor: jrrdw » Fri Oct 13, 2006 4:44 pm

Where did this - " ...50 mph is 73 mph, and 0 MPH is NOT 7 fps" come from?

I never said that, what i'm saying is, if your driveing 50mph you measure fps by doing this, - 50 (or any speed your driveing) divide by 2, gives you 25, add 25 to 50, = 75, add 7,= 82, your traveling 82 fps.

example 2 - your driveing 70 mph, divide by 2, = 35, add 35 to 70, = 105 +7 = 112, at 70 mph your travling 112 fps.
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Unread postAuthor: boilingleadbath » Fri Oct 13, 2006 5:31 pm

Yeah, except it's not true.

1) it's a good bet to question anything that tells you that a stationary object is acctualy moving.

If you solve your equation for 0 mph, you find that the object is moving at 7 fps (0 + .5*0 + 7). So a stationary object is... not stationary?

2) There are 5280 feet in a mile, and 3600 (60*60) seconds in an hour.
Thus:
1 mile/hour * 5280 feet/mile * 1 hour/3600 seconds = 1.46666 feet/second

1 mile/hour thus equals 1.4666 feet/second
(and if you solve this, you'll find that 50 mph = 73 fps)
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Unread postAuthor: MrCrowley » Fri Oct 13, 2006 5:43 pm

and 70mph is 102fps not 112fps
70x5280/3600=102.6fps
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Unread postAuthor: jrrdw » Fri Oct 13, 2006 6:22 pm

How do i explain this more clearly?.....O.K. - We are not talking about moveing 0 mph. You are adding 0 mph in where it don't belong, after all if your doing 0 mph, your doing nothing, so there is no equation. Not untill it whatever it is, starts moving.

And yes it can be that simple!

Give you credit for something you mentioned, the wind friction does slow it down, there for makeing the equation ever changing untill it stops moveing.
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Unread postAuthor: MrCrowley » Fri Oct 13, 2006 8:31 pm

yeah but the equation still doesnt add up
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Unread postAuthor: boilingleadbath » Fri Oct 13, 2006 9:22 pm

Zero is a perfectly legitimate entry into such a unit-conversion formula.

...anyway, I'd like to see even one website that uses values that could be generated by your equation.
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