BB Velocity Estimator

[Fresh]

I was wondering if there is some type of quick calculator that can take the initial velocity of a bb with weight involved and estimate the velocity at a certain distance from the barrel. I was mainly wondering because of engagement distances, i.e. if we use a .20 @ 400fps, whats the fps at 50 feet? I know that I could eventually figure this out using physics by kinetic and potential energy change and fluids using bernoulli's principal but that’s too difficult for airsoft. Any input?

[Wallace]

This has been discussed in ARRCO before, however due to the complexity of aerodynamic, especially with the top-spin, we will need some multi-billion fluid dynamic simulation program to calculate that. In addition, as you've already hinted on, the weight will play a major factor into the calculation as well, because when using the same gun, a heavier BB will hurt more down range simply because it retains its energy better by lowering its muzzle velocity. To be more accurately put, friction is a power of speed so the faster the BB goes, the faster it lose its energy due to air friction. Although the initial energy will be similar, the impact energy down-range is what we are really interested in, and different weight BBs will have different impact energy down range due to muzzle velocity differences (hence friction differences) even if the same gun is used.

That being said, the best alternative is just to setup two chronos at various distance and shoot BBs through both of them, as suggested by Hardlock. That still needs to be done...



Ez.Wallace

[Fresh]

Well, if I had a chrono, I might do it, but I dont have a chrono. Would anyone be interested in trying this out for .20 bb's just using distance increments of 10 feet which would give a good appoximation for estimating inbetween values?

[Wallace]

Originally posted by zinger084
Well, if I had a chrono, I might do it, but I dont have a chrono. Would anyone be interested in trying this out for .20 bb's just using distance increments of 10 feet which would give a good appoximation for estimating inbetween values?

Well, I had also planned to do it for a long time but... as you know... things always comes up. :p



Ez.Wallace

[almega]

awesome post wallace :)

anyway, 535-545 fps with .2, will be about 400-430 fps at 50 feet. I did that "test" a while ago with my m24, not saying that you could take that data and make any assumptions (i'm sure you cant) but you asked so there ya go :)

[Wallace]

Oh by the way, I think if safety is the concern, it will be more meaningful to test impact energy using high gram-weight (0.36g?) BBs because in theory they will have higher impact energy down-range then lighter BBs. Just a thought.



Ez.Wallace

[D-Boy]

If you buy a chrono make sure it works with airsoft. My friend has one for paintball and we tried it on our aegs and it did not always read. This is to the ovious size of the projectile and it being built for 68 cal paintballs. It will read 1 out 5 times on a good day:D. Well it is better then nothing when you got dishonset ppl about fps to still have full auto.

[Kaiser78]

D-boy,
It could also be that a paintball chrono usually tests for air pressure not velocity over time/distance. For those chrono's I found that it would always read properly if I used a GBB right near the muzzle. AEG's didnt work at all due to there being no pressure being released. In a paintball gun the principal is the same as it is with a real firearm, the size and placement of the holes in and round the flashhider expel the gas which is what those chronos read.

[Wallace]

Originally posted by Kaiser78
D-boy,
It could also be that a paintball chrono usually tests for air pressure not velocity over time/distance. For those chrono's I found that it would always read properly if I used a GBB right near the muzzle. AEG's didnt work at all due to there being no pressure being released. In a paintball gun the principal is the same as it is with a real firearm, the size and placement of the holes in and round the flashhider expel the gas which is what those chronos read.


Hum now that's interesting, in my old paintball days most of the chrono are radar-based and since BBs are too small the radar couldn't pick it up (especially the handhald ones). But the "big red" can read them just fine, however the big red needs to be calibrated occasionally and can also be easily "cheated".

Anyhow, if you got one of those optical-based chronos (have two sensor and you install the white diffuser using two metal rods over each sensor), make sure you have enough lights directly on top of the chrono, and the diffusers are installed. When I said enough lights, I am talking 2x 100watt bulb directly on top of the chrono. Otherwise they don't read (unless you got the indoor lighting kit or LED kit). Also, try to shoot as close to the senser as possible (i.e. place your muzzle as low as possible), it will help them read better. Just be careful don't shoot your own chrono!

Hope that helps.



Ez.Wallace