Chrony Conundrum

[CDN_Stalker]

Been doing a crap load of testing with my new Chrony F1 since december, in my basement, and have been seeing really odd issues from night to night. I have it set up under a regular bulb, and have the diffusers on to make it actually work every shot.

What I've noticed, at first with my CA M24, is that one night it'll chrony at 525ish, and all rounds tested sit within 5-10fps of that, the next night without any changes it'll chrony 508ish, next night 487ish, next 505ish, etc. etc. Been noticing that with my MP5s as well, one I downgraded and had it shooting pretty well between 320-330fps, two nights later it was 300-305fps. My other one I spent all weekend rebuilding it, and once done had it sitting quite happily at 385-395fps, got a couple 398, 399s in a string of 20odd shots, then one 403fps. Totally legal for field use. Next night I ran 10 or so shots through it, the lowest I got was 410fps and the highest was around 418fps or so.

Funny thing, I test BB Bastards with my TM MK23 springer and it NEVER changes, always sits around 215-220fps with 0.20g. Not sure if what is varying is where I put my shot through or not (MK23 is always shot consistantly because it's shot and easy to aim over the sensors, but the AEGs and bolt action are difficult to get consistant paths with. And I don't think light is having much effect since I did a bit of chronying with my MP5 using sunlight and it showed similar results. And it's a recently installed battery (albeit cheap ones, don't know if these require high quality ones or not).

Any thoughts? Nothing changes from night to night except maybe the temperature (is my basement, unfinished....... )

[Jimski]

temperature, humidity, I bet these are going to affect compressed gas behavior.
...that could affect tightbore barrels too.

store your guns in some other (warm and with constant humidity) room one day, make measurements and do the same thing a few days later - compare ?

[Renegade)]

Gremlins?

[CDN_Stalker]

Originally Posted by Jimski

temperature, humidity, I bet these are going to affect compressed gas behavior.
...that could affect tightbore barrels too.

store your guns in some other (warm and with constant humidity) room one day, make measurements and do the same thing a few days later - compare ?

Well, I doubt either of those would have much of an effect. My basement doesn't really change much form night to night, maybe a few degrees at the most. And it's my AEGs and M24 (spring) that are affected, not my springer (which is the odd part). This is obviously not a simple issue, it has to be even more complex than I can even figure out at this point (I'm no rocket scientist, but all I can even think how slight changes in humidity and temp can alter the fps that much without any other changes is the compressability factor).

[m102404]

I'm assuming that you're using the same BB bastard BBs through your rifle and other guns?

The sensors of a chrony work on detecting a drop in light (photon mumbo jumbo) hitting the receptor (i.e. the shadow of the bullet/bb)...so the following can affect it:
1. Dust in the air
2. Incidental shadows (i.e. the light from the stairway was giving me screwy readings once)
3. Intensity of the light (i.e. my old red shooting chrony doesn't have any smarts and I'll get different readings if there's just barely enough light to get a reading vs. a good strong source of light)
4. Dust in the sensors
5. "Shadow casting" nature of the projectile

2/3/4/5 would be consistent during a given shooting session...1 could vary depending on whatever is going on at the time (I do woodworking as well and it plays havoc with electronics).

Ideally you would have a light positioned directly (and diffused) over each sensor and high enough so that the light from one bulb wouldn't be able to hit the other sensor directly (this happens to mine if the bulb is over the rear diffuser...it kind of shines un-diffused? onto the front sensor).

I've set my chrony up in an old tool box with a backstop box inside. It tends to help with the consistency of chrony-ing in my basement. The light is positioned more towards the front sensor so that the rear screen "screens" the rear sensor.

But I think I'm going to throw in the towel...and get one of the madbull chrony's from Jugglez. I'm getting tired of setting it up and just want to stick the muzzle a set distance away from the front sensor and pull the trigger. (Plus...I want to see what the ROF of my CQB rifle is... )

All of the above probably doesn't help...but I hope it does.

Tys

[CDN_Stalker]

Taken a lot of that into consideration already and doesn't really sort out, more so why two MP5s and one spring bolt action are fps affected, but same time and conditions the MK23 springer isn't affected at all. Unless it has something to do with the higher fps guns and not the lower ones.

[Jimski]

humidity? atmospheric pressure?

how is the system in your springer ? could it be more air-tight?

[Styrak]

Get a better chrony. :P

One with a self-contained light source and tunnel.

[CDN_Stalker]

Well, i got one of the best and most consistant ones out there, the same one used at most fields too, and don't feel like spending more than the $110 I already did. It's a real steel Chrony, not a crappy cheapo one.

I think I'll pick up some cheap LED lights and place them on the diffusers and see if that changes anything.

[m102404]

Maybe the springer, chrony and BBs are fine...but your other builds are shit? (JUST KIDDING.......)

When you get a different reading with a given rifle...do you still get the same variance (+/-fps)?

I definitely get different reading depending on how close the muzzle is to the front sensor or how high/low it is.

Trick 1: tie a pipe cleaner or bit of wire to your chrony and have it come out towards you and up to where you want your muzzle to be...then just get your muzzle to touch it and shoot

Trick 2: set it up in a shooting box (or on a table) and rest the rifle on the workbench. just make sure you have a good bb trap

[m102404]

Originally Posted by CDN_Stalker

Well, i got one of the best and most consistant ones out there, the same one used at most fields too, and don't feel like spending more than the $110 I already did. It's a real steel Chrony, not a crappy cheapo one.

I think I'll pick up some cheap LED lights and place them on the diffusers and see if that changes anything.

Let me know if the LED thing works....I'm not much of an electrician but do they "flicker" like fluorescent tubes (which don't work, at least for my chrony)?

Tys

[Styrak]

Regular lights flicker too. Power is 60Hz.

[CDN_Stalker]

I've been using the Crosman BB trap, works great!

Am sure you've seen my thread on BB Bastards, I've posted readings there, a couple M24 ones and a couple MK23 ones. I don't vary my muzzle distance much, generally I'll fire a few inches from the first sensor, then move the gun out of the way to check the reading, then next shot (AEGs that is). M24 I have to cock every shot but still try to hold it in the same position each time.

LEDs don't flicker, they are constant, but not sure if the frequncy of light is a Happy Meal for the sensors though. I'm gonna try some checking out using LEDs on the diffusers and such. Could be interesting troubleshooting a chrony set up instead of three months solid of guns, guns, guns.

[Jayhad]

Stalker I have the same chrony and when shooting indoors I use a quality flashlight at about a 45 above the rear sensor... seems to work very consistantly. Using regular light I get errors and inconsitant readings.

Styrak as to your comment about getting a quality chrony..... you are a noob
F1's are THE BEST chronys on market I'd like to see your Madbull read anything over 750FPS let alone the 7000 FPS the chronys will read

[Styrak]

I just meant about the light source. I know those kind of chronies are finicky with light sources.