Homemade Chronograph

Shigsy

I'd like to test the FPS rating of my new gun when it arrives tomorrow, but im not willing to fork out €100 on a chronograph (sample price, based on cheapest Gizmos have).
So has anyone got any techniques to accurately measure the FPS of an Airsoft gun? I think i've seen people mention a basic test using a coke can, but im not sure how accurate this is. Anyone got any techniques they use?

I was thinking of something like this:
Id get a block of styrafoam and set it up at a set distance (say 10ft). Then get 2 guns that had been chrono tested so id know the exact FPS of each (the actual FPS, not what the box happens to say). Something like a 300fps gun and a 200fps gun would be perfect. Then i could fire into the foam block from 10ft and measure the distance each travels into the block. So for example, say the 300fps BB traveled 30 inches into the block and the 200fps BB traveled 20 inches into the block, then i could use this as my gauge for any new un-chrono tested guns. So if my new gun travels 25 inches into the foam block from 10ft away, i know its 250fps.

(Obviously i made these figures up to make my example nice and easy, so dont reply saying 'those figures are way off' )

Sparks

€100 sure is a lot.
$26 however, isn't.
You need to look around more for gear:

http://cgi.ebay.com/RADARCHRON-Chronograph_W0QQitemZ300023799956QQihZ020QQcategoryZ10554QQrdZ1QQcmdZViewItem

ditpaintball

If you are near dublin, trinity paintball society have a chrono. They could help you out. You may ask them.

Shigsy

Sparks wrote:

€100 sure is a lot.
$26 however, isn't.
You need to look around more for gear:

http://cgi.ebay.com/RADARCHRON-Chronograph_W0QQitemZ300023799956QQihZ020QQcategoryZ10554QQrdZ1QQcmdZViewItem

Thats 2nd hand, there is over 4 days left, and the reserve hasn't been met... All-in-all, i can see this going for a hell of a lot more than what its at now. You cannot use ebay to gauge prices unless the auction only has a few hours to go.
Anyway, i like the Trinity idea but keep your suggestions coming. Id like a good homemade idea

Sparks

Yeah, that auction might not go for €26. Search for chronographs in eBay's sports goods section though, and you turn up pages of results, most for less than €100.
And there's nothing wrong with second-hand gear. Besides, if you were rich enough to look down your nose at second-hand stuff, you'd just buy a brand new chrony and not start this thread in the first place, wouldn't you?

Shigsy

Sparks wrote:

Yeah, that auction might not go for €26. Search for chronographs in eBay's sports goods section though, and you turn up pages of results, most for less than €100.
And there's nothing wrong with second-hand gear. Besides, if you were rich enough to look down your nose at second-hand stuff, you'd just buy a brand new chrony and not start this thread in the first place, wouldn't you?

I wasn't really planning on buying one at all to be honest, because ill most likely only use it once or twice. If i find a cheap 1 on ebay i suppose i might get it. What do people currently do to check their fps? How does the coke can idea work? What power is needed to go through a coke can at what distance?

kdouglas

try this: http://www.airsoftretreat.com/features/articles/the_poor_mans_chrono/

kdouglas

or this: http://www.seattleairsoft.com/modules/news/article.php?storyid=15&page=0

ditpaintball

the coke can idea requires a lot of work before you can start to record fps accurately. Depending on how patient you are and your maths skills, it would be a while. To be honest, i dont think it would be accurate enough anyway.

If you were 90% accurate, that is 330fps or 270fps if you are aiming for 300fps. A 60fps margain.

Shigsy

Thanks kdouglas, that 1st link is the kind of thing i wanted. When i get my gun tomorrow ill try out this experiment and post my results here.

I still think my 'foam block' idea would give a more accurate reading, but i'd need to chronograph 2 seperate guns 1st to get the distance between them.

kdouglas

not sure how reliable the density of styrofoam would be, but the second link i posted using two microphones sounds a bit more reliable

Shigsy

the 2nd link wasnt working yesterday so couldnt try it out. Works fine now, had a read and it does sound like an accurate method. Think ill give that a go Supposed to get my gun today, should be able to do a fps test over the weekend at some stage so ill keep you informed.