Chrono Certification

[Pezco]

I have and use a CED M2 chrono and have noticed about a 50fps drop when I use the light box vs. ambient light. The difference in my MG121 IFP in my Bedell 38SC shorty is consistently a change from 172 to 166 PF.

[XRe]

The original answer to Bobby's question is: there is currently no requirement to calibrate the chrono. Realize that calibration means to compare the unit against a standard (ie, a known quantity reference value of some type). Calibrating a match chrono would require sending it off to a lab, and having them compare it to a reference standard, confirm that it's within certain narrow tolerances, etc - and then the chrono would have be used under the exact same set of procedures and circumstances to insure that the calibration is valid (which means calibrating for every bullet type, etc, too, BTW...). This is an expensive process that would have to be repeated at regular intervals (say, a year?). This renders the whole process impractical.

The rules suggest using two chronos in tandem, with controlled lighting conditions (that is, a chrono coffin arrangement of some flavor), and give stipulations for how to give the benefit of the doubt to the shooter (ie, use highest value between the two, etc). However, two chronos is not a requirement. You'll note similar suggestions for scales.

Scales are to be calibrated with check weights each day, per the scale manufacturer's instructions.

In terms of verifying that the chronos seem to be working, the chrono staff is required to follow a procedure that establishes a baseline value for the chronos and then stays fairly consistent from day to day. This also allows them to validate the chrono mid-match should a competitor protest it, etc. When shred and I wrote Appendix C2 (yes, we wrote it... George Jones submitted it, and it was edited some from there), +/- 4% on the chrono values was the best we could get passed. Yes, that means the chrono is allowed, under the rules, to wander enough that your 170PF ammo is suddenly 163PF ammo, and the chrono is still valid. Yes, that is a sick joke

In practice, it's hard to say that it ever becomes an issue - this is because the vast majority of folks show up, make the PF they desire, and move on, even though their PF may vary a bit from what they expected. In some cases, this is truly user error, and folks learn a hard lesson at the chronograph. In other cases, we don't really know - it could be some strangeness with their load and the environmental conditions - but it could also be some phenomenon with that chronograph.

In practice, if we were to use old school paper/wire chronos (they used two sheets of paper, impregnated with a wire that would be cut by the bullet passing through the paper - no electric eyes involved, etc), it would be a much more accurate process - but chrono'ing would take longer due to switching papers for every shot, and it would be expensive to buy the materials for each match, etc. So, as Mark said above, we do the best with what we've got...

The worst part of is that the chrono will never - ever - catch a determined cheater (at least, not the normal stop at the chronograph - only the RM pulling someone who appears to be cheating, and running them past it a second time has a chance of that). All it can ever hope to do is punish the unaware or unlucky...

[lcs]

A6 had 300+ shooters and all went through the chrono. If the chrono was bad, then a lot of folks would have gone minor or subminor.

I have been at one match where the chrono stage was thrown out because way to many people went minor or just squeaked by. So it can happen. This match only had one chrono though.

[wgnoyes]

... and doesn't have to be mounted in a silly box.

The "silly box" is actually a rules requirement from Appendix C2.

The chronograph(s) must be shielded from the effects of changing sunlight.

Setting the chronograph(s) in the shade of a tree, or under a cover which

allows a differing amount of sunlight to touch any part of the skyscreens or

skyscreen brackets is prohibited. The recommended method for outdoor

locations is to use an enclosed “chrono box”. In all locations, the use of

either infrared sensors or incandescent lighting provides the most consistent,

repeatable results.

That, I believe, was the basis for the chrono being thrown out at the 2009 AL state championship; it wasn't shielded from varying light conditions as the day progressed.

[XRe]

... and doesn't have to be mounted in a silly box.

The "silly box" is actually a rules requirement from Appendix C2.

It's a rule suggestion, not a rule requirement... The only requirement is that the chrono be given consistent, even lighting throughout the day, per your quote... However, the chrono coffin is really the only way to insure consistent lighting and, in my opinion, should've been made mandatory...

[Mark K]

I was performing so poorly, that it did not matter if I was Major or Minor. My question to Bobby that day, was mostly how could this happen? I attributed it possibly to the fact that it was quite cold that previous night and probably in the 50s when tested first thing in the morning.

I DO NOT CARE ABOUT THAT RESULT. Everyone was tested across the same chrono. The testing was fair. My concern was my own - how could I depend on a legal Major load.

Mark K

I've got a compound questions: Shoot the match in one day or two? Did your chrono ammo spend the night, i.e. collected on day one, shot early on day two?

I shot two days. Ammo was collected Saturday Afternoon, and we shot the chrono about 8:30am Sunday.

BTW, I had them shoot the last bullet.

Mark

Edited April 29, 2010 by Mark K

[wgnoyes]

... and doesn't have to be mounted in a silly box.

The "silly box" is actually a rules requirement from Appendix C2.

It's a rule suggestion, not a rule requirement... The only requirement is that the chrono be given consistent, even lighting throughout the day, per your quote... However, the chrono coffin is really the only way to insure consistent lighting and, in my opinion, should've been made mandatory...

No, I'm sorry, it's a requirement, that is, some device that shields the chronograph from varying sunlight.

Appendix C2. The chronograph(s) must (emphasis added) be shielded from the effects of changing sunlight. ...

And as you say, an all-enclosing container box seems the best way.

I suppose you could turn a couple of barrels on their sides and instead of a silly box have a silly cylinder?

But you gotta have something.

Edited April 29, 2010 by wgnoyes

[proff]

If the chrono isn't perfectly level the pickups are ever so slightly closer which would cause a high reading.

[XRe]

And as you say, an all-enclosing container box seems the best way.

I suppose you could turn a couple of barrels on their sides and instead of a silly box have a silly cylinder?

But you gotta have something.

Putting the chrono under cover (tent, or permanent shelter arrangement...) that prevents any direct sunlight from ever making contact with the skyscreens and brackets throughout the day also satisfies the requirements (though, as we both agree... not very well). You could also go to the efforts we did at the '98 GA Sectional to arrange targets over and to the side of the chrono to prevent direct sunlight - an even less optimal solution, but it "works" under the rules.

This was another one of those edits that were made to the original work, IIRC Roy and I wanted the coffin to mandatory, but I guess that was too restrictive... Personally, I think any part of the rules that can negatively impact your match score by 10+% should be a little bit restrictive - especially when the equipment involved and the operation thereof is a little bit akin to voodoo...

BTW - the rewrite came about because we watched a couple of people get abused at the chrono station due to procedural problems, and we got tired of seeing it happen (it didn't happen to either of us, for the record). We saw one shooter have a bullet turn up a couple of grains light, making him go minor - the scale was a beam balance being used in 15-20 gusts without any kind of wind shield. Another shooter was competing in Production and went sub-minor - his ammo was left out all night in freezing weather and he was chrono'ed first thing in the morning. Same ammo, same chrono, later the same day, and he was 130 PF. It's appalling how error prone the chrono can be if it's not operated properly - hopefully, the rule changes have at least helped in that regard... I'd still like to see them be tighter, though...

Edited April 29, 2010 by XRe

[Sarge]

I use sub-minor ammo in the 115 PF range. Each morning the same lot of ammo is fired over the chrono and the results are recorded. If it varies by more than 4% the chrono will possibly get tossed for that match.

See appendix C2 for all relevant details.

========

I forgot to add how entertaining it sometimes is for folks to lose a popper calibration challenge and learn it just fell with sub-minor ammo. There were a couple of times I wish I'd had a camera.

But how do you know that it's 115pf ammo?

Using 2 chronos back to back does help validate things. I know there are some folks that are "traveling chrono guys" and always use the same chrono and I've only heard of one match with the chrono stage getting thrown out.

Bobby, I have always wondered the same thing. When I first bought my chrono I think I even asked the same question. I am not adding or taking anything away from this debate/discussion. But I assumed there was a way to calibrate a chrono.

[Sarge]

It truly seems that sometimes there is just no logic to the chrono readings no matter how much you study the subject.

I was right behind Mark at chrono @ A6. I had loaded some titegroup loads that actually were overkill according to my chrono two days earlier(139+)at 70 degrees. It was cold the morning of A6 chrono and I told myself it was a good thing I did load a little hot since it is so cold my TG loads will certainly be slower. NOT!! I came in at 141! So for me it seems that it just don't make sense sometimes.

[XRe]

It was cold the morning of A6 chrono and I told myself it was a good thing I did load a little hot since it is so cold my TG loads will certainly be slower. NOT!! I came in at 141! So for me it seems that it just don't make sense sometimes.

TG is apparently reverse temperature sensitive... Cold weather is your friend with that powder

[kgunz11]

I don't know if Mark's ammo was left out overnight so that it could reach a 50* ambient temperature and that effected the results, but it could of happened. As for you Sarge, some powders get faster as they get colder. It's called "reverse temperature sensitivity".

[Sarge]

It was cold the morning of A6 chrono and I told myself it was a good thing I did load a little hot since it is so cold my TG loads will certainly be slower. NOT!! I came in at 141! So for me it seems that it just don't make sense sometimes.

TG is apparently reverse temperature sensitive... Cold weather is your friend with that powder

I have always read or heard the opposite. TG is temp sensitive. Solo is reverse. No?

[XRe]

I have always read or heard the opposite. TG is temp sensitive. Solo is reverse. No?

It's listed in Guy Neill's article with a question mark - meaning he got less than conclusive data on it. N320 is in the same boat, but my experience is that N320 is strongly temp sensitive in the normal direction, which would match the conjecture from Hodgdon re: why they think reverse temperature sensitivity happens (fracturing of powder granules with double base powders - Guy notes that several single base powders made his list, though, so it may be more related to granule shape...)

[juan]

How about we rethink the way we measure power factor.

instead of bullet weight x bullet speed.

how about we measure free recoil energy in a ransome rest.

something easly checked and calibrated

[wgnoyes]

The thing is, with a box, you only have to build it once. We didn't build a new box for Area 6 this year; we used last year's, design for which came from Ken Skeeters, who is the acknowledged best in the business.

Now, when another shooting discipline comes along and decides that their idea of a cleanup day is to burn everything that isn't nailed down....., well.....

[BlackBuzzard]

Chrono makers SHOULD specify accuracy and precession of their products..............they dont and this is unacceptable in any science or engineering method.

• In the fields of engineering, industry and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to its actual (true) value. The precision of a measurement system, also called reproducibility or repeatability, is the degree to which repeated measurements under unchanged conditions show the same results......from wikipedia
  

My wild guess on chrono accuracy? +/- 4 percent.

The only way to be safe is to load hot......172 at least for major.

BB

[aztecdriver]

How about we rethink the way we measure power factor.

instead of bullet weight x bullet speed.

how about we measure free recoil energy in a ransome rest.

something easly checked and calibrated

Curious question - but how would this apply to Open guns? Comps will clearly alter this unless I'm completely missing what you are saying. Then - will we have to have different rules for Open vs. the rest of the world?

[kgunz11]

My chrono is guaranteed to have less than 1% error, or be within 1% accurate.

http://www.neconos.com/details12.htm

[Skydiver]

My chrono is guaranteed to have less than 1% error, or be within 1% accurate.

http://www.neconos.com/details12.htm

Can we get a USPSA member discount of... say about $550... to bring it down to the same price range as a CED M2? :-)

[SLM]

Looks like a nice one there Bobby. If you could the three different chronos (yours, a CED and the SC) in tandem and post the results that would be great!

[kgunz11]

My chrono is guaranteed to have less than 1% error, or be within 1% accurate.

http://www.neconos.com/details12.htm

Can we get a USPSA member discount of... say about $550... to bring it down to the same price range as a CED M2? :-)

LoL, you get what you pay for.

[kgunz11]

Looks like a nice one there Bobby. If you could the three different chronos (yours, a CED and the SC) in tandem and post the results that would be great!

If they are all available I'll do that. I'm also going to take some of Mark's ammo and put it on ice for a while and see if that changes things much. Clay's does make me a little nervous though, it's too dangerous to muck with.

[Skydiver]

On the original question of calibrating the chrono, can we have a device that sends a projectile through the chrono at a well known speed? The device will have to based well known constants and principles like the acceleration due to gravity, or the forces exerted by a spring. Of it not a device that sends a projectile at a known speed, something to measure the speed at impact?

Gravity: I can't figure out how to get an object moving fast enough for the low end a chrono's range with using gravity without some kind of mechanical advantage. Looks to be a complicated device.

Spring: I can conceptualize a ball bearing being shot out of a tube by a spring. Using Hooke's Law, the force on ball can be computed, and therefore the "muzzle velocity" can be computed and verified against the chrono. I don't know if springs are strong enough to get to the low end of a chrono's measuring range.

Collision: I can see the return of a more sophisticated ballistic pendulum. If the mass and length of the pendulum is known, and there is a way to measure the maximum swing of the pendulum after being hit by a bullet, then the force needed to move the pendulum that far can be computed. From the force, get the instantaneous deceleration. From the deceleration, get the velocity at the moment of impact. The bullet should not have slowed down dramatically from the time it went through the chrono to the time it hit the pendulum.

I'll leave it to the true engineers and geeks to figure out the exact details. :-)

(Can you tell I just remember enough of general physics and mechanics, but not enough of applied physics? LOL!)

Followup: Looks like Ackley's ballistic pendulum already has the details figured out. :-)

http://en.wikipedia.org/wiki/Ballistic_pendulum#Ackley.27s_ballistic_pendulum

Edited April 29, 2010 by Skydiver