SpudFiles

I've been trying to get some velocity readings on a little "project".

Specs aren't too important for the question, but what the heck.


Barrel: 36" of 9/32" brass tube, .014" wall, fits 6mm airsoft bb's quite well

Chamber: 6" of 3/4" Type M copper

Piston: Machined from nylon with a sealing face of teflon. "Spool" shaped for weight reduction and using a floating o-ring seal

Co-axial configuration

Pilot: The modded blowgun and fittings from my copper gun. The bumper was "borrowed" as well.

Operating pressure: 400psi air

The problem is that the airsoft bb's are not registering on the chrony.

I checked and changed the battery, and verified it was working with a .177 air rifle.

Firing a shot with the air rifle, leaves a fps reading on the chrony. Following up with a shot from the "project" doesn't change the reading indicated.

I am not getting error messages as when only one sensor reads the projectile. (It does however, penetrate ~3/8" into the phone book/backstop. )

I am getting a no reading what so ever, on the dozen shots fired thus far.

Anyone have any ideas as to why?




Edit: I know Jack had a similar (errors?) problem with a combro chrony and was going to try an F1.

I'm using an F1.

I know it might sound stupid.... but maybe the round has to be made from metal ??

At this point, I'll take ANY ideas for consideration.

I'm not sure about that, it worked fine when I was testing both the copper gun with marbles, and the pvc gun with marshmallows.

I think the sensors pick up a change in the level of light, but I'm not 100% sure.

Could it BE light related? But then WHY do the .177 pellets get noticed?

They are smaller than the bb's.

The mystery deepens.

Just a thought but at that velocity maybe the trajectory is going above the gauge?
Sounds like a cool project. (Pics?)
But you hacked your copper gun(?) 8)

The chrony is supposed to read up to 7000fps.

If I'm exceeding that,.. I guess you can start bowing now.

Seriously, it should be close to mach 1, but no where near the limits of the chrony.

I'll be posting it when I'm happy with it. I still need to give it a polish.

As to the copper gun, I just "borrowed" the pilot assembly for now.

I have started a new and better copper gun. (Chamber sealing piston with bolt action. ) And likely WILL chop up the old one to free up space.

This might help:

http://www.nodakoutdoors.com/forums/vie ... hp?t=51970

Normally these things work on an infrared beam. Have you tried both with and without diffusers?

It might be possible that the BB isn't blocking the beams for long enough to trip it. A .177 pellet is usually somewhat longer from head to tail than a BB, and I'm guessing, not quite as fast as your project is spitting out BBs (what was the air rifle coming in at?).

After all, the chrony is usually asked to detect projectiles which are rather longer proportional to their speed (and thus block the sensors longer).

Try using a lower pressure (and thus velocity) and see if it starts registering then. If not, obviously it's not that it's too short a blip for the chrony.

Try using colored BB's, I think it may be made out of the same plastic the little upper spars are. That is, if the one's you're using are white.

Good ideas, thanks!

I'll try the diffusers tomorrow, and paint my red bb's black.

Lower pressure doesn't sound like as much fun, ( ) but I'll try that too.

try looking at where the detector's are, and shoot directly above it.

Gippeto wrote:Lower pressure doesn't sound like as much fun.

It won't be of course, but it's a means to diagnose the problem.

I have results now.

I painted my airsoft bb's black with a sharpie pen, used the diffuser screens, and the indoor light kit.

Readings varied between 1205 and 1239fps. 8)

According to wikipedia, sos in air @ 20C is 1125fps.

Gippeto wrote:Readings varied between 1205 and 1239fps.

According to wikipedia, sos in air @ 20C is 1125fps.

I'm going to have to ask it, or someone else will - how close were you to the Chrony?
It's not impossible to go supersonic pneumatically, but it's very improbably - and extraordinary claims require extraordinary proof.

Also, you've just made me realise an error in the LRC - now fixed.

Oh come on, show us the launcher

I did manage to get readings for 6mm BBs with an F1 and they were light yellow, glad you managed to find a solution

@ Rag;

Within roughly 6". I'll be taking a video later to include when I post it.

I trust that will be satisfactory evidence?

Coming soon to a thread near you.