Chrono questions...is it out or not?

[Egon_247]

So, i fitted one of Ak2m4's super-duper barrels to my boys mp5 a few weeks ago and then chrono'd it using my little silver chrono.

Was showing 1j there or thereabouts. cool.

we get to site on saturday and go through chrono and the guy tells me its lobbing 0.28's at 0.65j.

Nothing has changed on the pew after my testing, even used the same housebrick of a battery.

Now either mine is off or theirs is off as you cant just lose 0.35j in the space of a few days, can you? 

Is there a way of checking them (without another chrono next to it, that might be a bit more of a challenge to check!)

It was shooting fine, range was 50m+ and other than changing out a poor feeding mag, had no issues at all.  

weird.

 

[Skara]

Did you chrono on 0.28s at home?

Some guns do lose an awful lot of energy by switching to heavier BBs

 

[Sewdhull]

Yours might be off a bit, theirs might be off a bit, temperature changes things. Stuff can happen do a gun, if you drop t maybe or stuff like that. Did you chrono it again at home?

 

[Egon_247]

Did you chrono on 0.28s at home?

Some guns do lose an awful lot of energy by switching to heavier BBs

Yeah, all my RIF's are running on 0.28's so it was good to go.

Yours might be off a bit, theirs might be off a bit, temperature changes things. Stuff can happen do a gun, if you drop t maybe or stuff like that. Did you chrono it again at home?

Strange, Yeah, its chrono'ing at 1j again at home. 

Maybe time to upgrade the chrono, i've had it a while now. 

Meh, more moneys..

 

[Tommikka]

There are many factors

Try two chronos against each other for multiple shots

The angle and proximity of a chronograph can get different results

If you’re using a gas based system then changes can occur with ambient temperature and also the rate of fire / length of refresh time between shots

Different types of chrono can get different results, even two of the same type/model may show a different result 

Chronographs try to measure the velocity of distance vs time, and where applicable Airsoft chronographs add the extra step of converting velocity to energy based on the entered weight / mass

 

[Egon_247]

Its an older G+G mp5 AEG. Yeah, i've seen the gbb pistols i have cause havoc with the chrono. too close and its snorting gas, giving all sorts of weirdness off.  

I shall endeavour to find a new one and test them back to back, i think. 

 

[Skara]

I shall endeavour to find a new one and test them back to back, i think. 

Find one that isn't yours nor the site's, you'll have a pretty good measure of which one is busted.

If you're in the market for a new one, then you may look at the Acetech 5000, it's essentially the good ol' Xcortech mk3200 but in a different casing and with a few more functions.

 

[Rogerborg]

This is why I take my chrono to site to compare it to the site readings.

 

[Shamal]

It's the same with blood pressure machines.

Tried three different BP units at hospital and all three gave different readings and my home BP unit gave another result.

The hosp just took an average of the three.

Hope that helps....NO!  

 

[The_Lord_Poncho]

I've had the same. In my case, it was midcap syndrome - i.e. i was just adding a few BBs into my mag for testing at home (lightly tensioned spring, no midcap syndrome), but loading the full mag up on the game day prior to chrono resulted in the FPS drop on the first few fired through the chrono from the highly tensioned spring in the mag.

 

[Lozart]

It's the same with blood pressure machines.

Tried three different BP units at hospital and all three gave different readings and my home BP unit gave another result.

The hosp just took an average of the three.

Hope that helps....NO!  

I was concerned that I might have the same issue until I had my BP checked at the docs and they used the EXACT SAME machine I have at home. So that's nice.

 

[NateChrony]

(full disclosure - I make chronographs)

0.66J vs 1J with 0.28gram is 225fps vs 277fps

That's a huge amount of difference in terms of timing.

Most of the manufacturing tolerances & timing uncertainty in designs is typically ~10-15fps when shooting 1000fps, with sensor spacing of 50-100mm or so.

50fps at that slow speed is something outside of a chrony's usual issues

If it was gas - that could definitely cause an issue, anything that is a liquid & expanding can leave a vapour cloud & cause issues with optical sensors - typically you get high readings as the vapour can move faster than the BB.

I'd say the chrony has a fault, take it to the field with you next time & compare side by side to rule out the conditions on the day.

You could also possibly open it up & see if you can clean the sensors - cue tip & alcohol should be enough.

 

[Lozart]

(full disclosure - I make chronographs)

0.66J vs 1J with 0.28gram is 225fps vs 277fps

That's a huge amount of difference in terms of timing.

Most of the manufacturing tolerances & timing uncertainty in designs is typically ~10-15fps when shooting 1000fps, with sensor spacing of 50-100mm or so.

50fps at that slow speed is something outside of a chrony's usual issues

If it was gas - that could definitely cause an issue, anything that is a liquid & expanding can leave a vapour cloud & cause issues with optical sensors - typically you get high readings as the vapour can move faster than the BB.

I'd say the chrony has a fault, take it to the field with you next time & compare side by side to rule out the conditions on the day.

You could also possibly open it up & see if you can clean the sensors - cue tip & alcohol should be enough.

Presumably, even at airsoft speeds, the further apart the sensors are, the more accurate the readings are likely to be?

 

[Skara]

Presumably, even at airsoft speeds, the further apart the sensors are, the more accurate the readings are likely to be?

Given a constant velocity, yes.

To have a 100% honest reading though, I guess the chrono needs to be setup in a way that the end of the barrel sits in the same exact position every time, relative to the first sensor and then needs to take into account the reduction in velocity given by drag, measured (or calculated) for each bb weight, in relation to the distance between the two sensors.

And then everything needs to be certified somehow so that the readings can be used, should the need arise, in legal matters.... Something nobody hopes to resort to.

 

[Sewdhull]

You'd want the sensors close to each other i think, so the measurement is less an average and more a snapshot.

Timing can be done accurately over short periods and since you're matching the speed of light with a bbs doing 500fps I don't think you want the sensors far apart.

The further apart the sensors are the more the averaging effect of the distance between measurement and the less you will see any differences in speed as they are lost to averaging.

 

[NateChrony]

Presumably, even at airsoft speeds, the further apart the sensors are, the more accurate the readings are likely to be?

yeah to a point (as others have noted) - as the wider apart you have them, the more the pellet/BB may be slowing down between them.

This could be even more pronounced with airsoft BBs - the BC may be very different.

Looking at rough size/spacing of common chronographs:

At Airsoft speeds (250fps) - its a pretty trivial task on the  electronics, you're talking ~500+ microseconds between sensors.

1 microsecond at 1000fps is the difference between 1000fps & 1008fps

1 microsecond at 250fps is about 1/2fps difference

Another way of of looking at it is tolerance of assembly/dimensions:

@200fps - 0.1mm = 0.2fps

@1000fps - 0.1mm = 1.25fps

The mounting is probably the most critical - i'm constantly amazed at how much vibrations & slight wobble have on the readings.

But this is when I calibrate at 1,000fps - expect something like a 5fps variance if there's bad mounting, thats why I chose muzzle mount.

 

[Egon_247]

Sooo.....

Tiny update as I hate threads that just die with no resolution...

Went again to our site and had a great day. His mp5 was chrono'd at 0.7j on .28's. checked mine against theirs and was pretty much bob on. Cool.

I used my G3 which was embarrassing and generally poo, but that's another story.

Through the day he lost power and eventually used the back up DE badger.

Yesterday I stripped it out and then realised that it was a "toptec" with the air cylinder blow back thing. 

So I swapped cylinders so no more blowback and on the SAME SPRING, chrono'd at 1.4j!!!! 

One point four. That's nuts. Also a tad illegal but I'm redoing the spring today. 

So remember kids: keep it simple. Blowback stuff on toptec is poo. Lol ? 

 

[Skara]

"toptec"

Ah yes, that genius idea from G&G to create a huge air leak to move a completely unrealistic and unnecessary part

Good riddance.

 

[Lozart]

Yesterday I stripped it out and then realised that it was a "toptec" with the air cylinder blow back thing. 

Ah yes, that genius idea from G&G to create a huge air leak to move a completely unrealistic and unnecessary part

Good riddance.

TopTech isn't the name for the flappy horrible pneumatic blowback. It's just the range of guns that had an MP5 with it on.

But yes, good riddance. Stupid idea.

 

[Egon_247]

Shootin' a healthy 1.05j consistent now with added MOSFET goodness with a three round auto. 

Just occasionally I get it right ??