What accuracy do you expect from a chronograph?

[fe7565]

What resolution and what accuracy do you expect from a chronograph? For airguns the velocity range is about 400-1,200fps a chronograph with a measuring accuracy of +/- 0.5fps-1fps is great with a resolution of 0.5-1 fps. What about firearms that can go as high as 4,000fps? What level of resolution and accuracy is realistic at that velocity?

Also, at what velocities are most shooters operating for target shooting? 2,800-3,200fps? What accuracy (+/- 1 fps?) and resolution (1 fps?) would you expect at those velocities from a chronograph?

 

[308pirate]

Is this market research or idle curiosity?

In general, most people's performance expectations for a product they buy are far out of proportion to what they paid.

Also, in what universe does an instrument that mere mortals can afford have an accuracy equal to its resolution?

 

[308pirate]

a chronograph with a measuring accuracy of +/- 0.5fps-1fps is great with a resolution of 0.5-1 fps.

Do you have a concrete example of this marvel in which its accuracy is equal to its resolution?

 

[fe7565]

I am hoping to build one for airguns, and maybe able to squeeze in enough velocity range for firearms too.

You will have an accuracy equal or better to its resolution if you over design it. For example, if I design the chrono to be accurate to +/- 0.25 fps and I set the resolution at 0.5fps or 1 fps.

A fairly "slow" 8Mhz MCU has a clock tick of 125ns. A 1,200 fps projectile measured between 3.5inch sensor gap registers at about 243.06us. That gives around 1944 ticks of MCU at 8MHz. 1201 fps would take 242.85us over a 3.5 inch gap, which is 1942.8 clock ticks (rounded to 1943). Doubling the 8Mhz to 16Mhz, would double the ticks to 62.5ns. So an antiquated 16MHz Atmega chip at 62.5 ticks would measure 3888.96 ticks at 1200fps, and at 1201fps it would measure 3885.6 ticks. That is about 3 ticks per 1 fps = 0.3 fps resolution.

Of course, today there are 70-600 MHz chip modules for sub $20 (Teensy 3,2 and 4.0 for example) which can have a tick as lows as 1.6-18ns resolution.

 

[308pirate]

You will have an accuracy equal or better to its resolution if you over design it. For example, if I design the chrono to be accurate to +/- 0.25 fps and I set the resolution at 0.5fps or 1 fps.

Maybe. I'm not an electrical engineer. What's your experience in designing data collection instruments (because that's what a chrono is).

This might help, maybe too basic for you: https://www.evaluationengineering.c...-vs-sensitivity-cutting-through-the-confusion

The processor is only a portion of the problem. I think where most chronos fail is in their input signal generation. I would personally would never buy another chronograph that relied on optical sensors to detect bullet passage.

Have you benchmarked the products available out there already? Labradar, Magnetospeed, and Oehler are the only three that can be taken seriously.

 

[fe7565]

Just hobbyist, learning as I am going along. Magnetospeed has a 1% accuracy rate, and of course Oehler is the benchmark for all chronos. The concept I am working on is similar to Magnetospeed, as far as using electromagnetic sensors, but it screws on the end of the barrel. Originally had a 5 inches sensor gap, but I brought it down for airgun speeds to a 3.5 inches gap. That leaves space for some baffles, etc as part of an airgun moderator.

The concept is already working, it has bluetooth (BLE), and have a simple Android app (for now no iOS). Still working on routing a (discreet) external antenna because the carbon fiber tube is an excellent RF-shield unfortunately, It has to be eventually miniaturized, because right now it is taking up a 4.5 inch long tube, and 1.4inch OD and mostly jerry rigged.

The same design of course for firearms works in theory, but I am not going there because of the limitation/laws on moderators. Also, the carbon fiber tube would not stand up to firearms pressures, so it would need to be metal. So again that leads to the law and permits/licences. Once I have the airgun version working, may try to test with placing the sensors on or near the (airgun) barrel, vs threading them on front. In actuality, it seems sensitive enough with pellets (so bullets should be even better) where it does not have to touch the barrel (bad for harmonics), but of course it would have to be mounted somewhere along the barrel length. Unless there is way to have them "levitate" magnetically around the barrel without touching it.

 

[308pirate]

Just hobbyist, learning as I am going along. Magnetospeed has a 1% accuracy rate, and of course Oehler is the benchmark for all chronos. The concept I am working on is similar to Magnetospeed, as far as using electromagnetic sensors, but it screws on the end of the barrel. Originally had a 5 inches sensor gap, but I brought it down for airgun speeds to a 3.5 inches gap. That leaves space for some baffles, etc as part of an airgun moderator.

The concept is already working, it has bluetooth (BLE), and have a simple Android app (for now no iOS). Still working on routing a (discreet) external antenna because the carbon fiber tube is an excellent RF-shield unfortunately, It has to be eventually miniaturized, because right now it is taking up a 4.5 inch long tube, and 1.4inch OD and mostly jerry rigged.

The same design of course for firearms works in theory, but I am not going there because of the limitation/laws on moderators. Also, the carbon fiber tube would not stand up to firearms pressures, so it would need to be metal. So again that leads to the law and permits/licences. Once I have the airgun version working, may try to test with placing the sensors on or near the (airgun) barrel, vs threading them on front. In actuality, it seems sensitive enough with pellets (so bullets should be even better) where it does not have to touch the barrel (bad for harmonics), but of course it would have to be mounted somewhere along the barrel length. Unless there is way to have them "levitate" magnetically around the barrel without touching it.

Just because you put a hollow tube over and in front of the muzzle doesn't mean you just made a suppressor. That's now how it works. If you were right, thousands of fullbore and smallbore rifle competitors using bloop tubes to extend sight radius without making the barrel excessively long would be felons. But they're not. You're making assumptions instead of understanding the laws.

So your device screws on to the end of the barrel...…..you need to rethink that. Nobody has a rifle with muzzle threads that do nothing. Those threads either have a sound moderator, flash suppressor, or muzzle brake screwed on them. And what about the millions of rifles without any muzzle threads at all?

 

[fe7565]

Wow..never even knew about the "bloop tube". Good to know that not everything that is mounted at the end of the barrel may be construed as a "sound reducing" device.

I agree with your about IR based chronos. They are easy to damage, because the LEDs are exposed and also very hard to clean. Some Daystate rifles had them back in 2008 (Airwolf MVT, etc) , mounted at the end of the barrel, but most people just removed them and disconnected then after they failed. Most failed due to user ignorance while messing with it, but the wire routing was atrociously dumb in the first place, like an afterthought. Daystate's latest model the Delta Wolf, about to be released next month, touts such a chrono. Same design, but they now have a clear hard plastic sleeve-inlet that protects the LEDs from bore cleaning, etc.

Thanks for the tips on broadening the potential appeal of the chrono. I wasn't actually thinking about the "millions of guns without a muzzle thread", because the vast majority of the shooters are not target shooting. I may be wrong but they probably care less if the bullet is at 2800fps vs 2900fps. I think this chrono would benefit those who are target shooting, tweaking, loading their own ammo where knowing the accurate velocity can help eliminate any other potential errors and also allows for a measure of progress.

In its simplest form, the chrono would be about a 4.5in tube that can be mounted at the muzzle end , thread or slide-over adapter, etc. Or, can slide/screw as an insert inside an airgun moderator and the the rest of the length/space of the moderator (6in-8in-10in) is taken up by baffles. However, I can make it a fairly small in diameter, a bit shorter, and have it hidden under the shroud. Or surround the barrel where its mounted inside the receiver block. Of course that would require manufacturer's buy-in.

The good thing is that airguns are easy to mod, redesign, and most gov regulations issues are not obstacles. And I really want to make it work for the airgun first in a reliable and solid way...before even thinking about adapting it to firearms. However, if I can incorporate in the design now some low hanging fruit ideas from your guys, it may save some future efforts for me.

So, what accuracy and velocity range would be useful for your (firearm) purposes?

 

[Thor2j]

Labradar is .1%. Dont think anybody cares about much more then that. Sure it would be nice, but best thing about labradar is no POI shift..

 

[fe7565]

Labradar is .1%. Dont think anybody cares about much more then that. Sure it would be nice, but best thing about labradar is no POI shift..

The Labradar is excellent, and probably the best broadly affordable commercial product. But setting up a fairly good size equipment and aiming, etc is not the same as to just pull the trigger and get your reading. And the Labradar is limited to 100 meters. It's great for BC of airgun pellets, albeit not very helpful for firearm bullet BC at 100 meter range only since you have to extrapolate the data based on that 100 meters and make some assumptions down the range 300-700 meters. Unless you setup another chrono near the target.

The POI shift is the main advantage of this chrono. If you already have a thread on the muzzle, you are going to put something there anyway. Anything you place on the barrel or touches the barrel can change the POI due to harmonics and air pressure turbulences. The harmonics (not as much the turbulence) is especially true for the Magnetometer.

So adding this chrono on the muzzle, or as an instead insert to the moderator itself, should not create a POI that was not there in the first place. If the chrono has proper characteristics (internal/mounting) like the moderator. But if the chrono is designed to hug the barrel inside the receiver block (airguns) there is no POI possible.

 

[6.5SH]

I'll say you are incorrect on that, all threaded objects on a muzzle are not equal. Look up what a barrel tuner does.

 

[fe7565]

I'll say you are incorrect on that, all threaded objects on a muzzle are not equal. Look up what a barrel tuner does.

What I am saying is that if you add something on the muzzle you would need to make sure that it does not change the POI. That is true for a moderator or a chrono, or muzzle brake, etc regardless. So the argument that this chrono can shift POI is just as true for a moderator, a muzzle brake, etc. It should not stop someone for adding it on if they already decided in the first place to add one "something" on the end of the barrel. I assume people tune their rifles for harmonics anyway, no matter what they add on the barrel end.

But, if the chrono sensors are placed before the barrel leaves the breach/receiver, there is no POI shift.

 

[Thor2j]

Problem is you are going after an audience that is all going to have something already threaded. Well it be a muzzle break, flash hider, mount for suppressor, nobody is going to have empty threads sitting there.

 

[fe7565]

Problem is you are going after an audience that is all going to have something already threaded. Well it be a muzzle break, flash hider, mount for suppressor, nobody is going to have empty threads sitting there.

I see. So placing the sensors before the mounting points of the barrel seems to be the only true no POI shift option. But that would require manufacturer's redesign, etc which is a mountain I do not care to climb. Not for firearms. For airguns, it's much easier.

For firearms, placing the sensors immediately after the barrel mounts (in the muzzle direction) in the first 4 inches would add potentially harmonics, but since it's so close to the barrel mounting points of the receiver, could that be considered as part of the manufacturer designs and part of the "natural" harmonics that needs to be "tamed" anyway?

Or, what about using the chrono as the harmonics tuning device on the barrel itself? In whatever position you would use any other tunder device along the the length of the barrel?

 

[6.5SH]

The rub there is barrels have a finite (though individual) "lifespan" for their peak (or usable) accuracy. So depending on the cartridge you can be using up something that may be gone in the course of only one season of competition.

 

[fe7565]

The rub there is barrels have a finite (though individual) "lifespan" for their peak (or usable) accuracy. So depending on the cartridge you can be using up something that may be gone in the course of only one season of competition.

Wow..! I was not aware of this! You guys have an expensive hobby! I thought airguns were pricey, but at least we airgunners get to keep our barrels !

 

[6.5SH]

BTW, I am not trying to discourage you. What you are doing is interesting but would need scaled up and adapted to the forces involved with actual firearms.

 

[fe7565]

BTW, I am not trying to discourage you. What you are doing is interesting but would need scaled up and adapted to the forces involved with actual firearms.

I appreciate the input, and the suggestions from all of you. I am still tweaking the electronics and wanted to make sure it's capable to scale up as far as accuracy for firearms. The current "prototype" hardware is for airguns, firearms are a whole other animal. But I want to make sure it works well with airguns before would even dare to consider to adapt it as a hardware for firearms.

 

[308pirate]

What I am saying is that if you add something on the muzzle you would need to make sure that it does not change the POI. That is true for a moderator or a chrono, or muzzle brake, etc regardless. So the argument that this chrono can shift POI is just as true for a moderator, a muzzle brake, etc. It should not stop someone for adding it on if they already decided in the first place to add one "something" on the end of the barrel. I assume people tune their rifles for harmonics anyway, no matter what they add on the barrel end.

But, if the chrono sensors are placed before the barrel leaves the breach/receiver, there is no POI shift.

Holy shit you are operating under so many assumptions that simply aren't true.

1. Very few people use harmonic tuners on their rifles. VERY FEW.

2. The POI shift caused by a muzzle brake/suppressor/flash hider is permanent. Meaning you add the device, re-zero your scope, and you're done. We don't normally take things on and off the muzzle all the time. A chrono that attaches near the muzzle is temporary and will create not only a transient POI shift, it can also change the barrel harmonics to the point where group size is affected compared to what it would be without that extra weight. This makes load development with the kind of chrono you have in mind a waste of time and money.

3. There are tens of thousands of hunters who take their shooting seriously, do reload, and do use chronographs. Most of them don't have rifles with muzzle threads at all. If you insist on a screw-on device you just eliminated a significant portion of an already small market.

4. Unless your chrono is as rugged as a chunk of barrel steel, I doubt many would want it permanently attached to the rifle anywhere. Plus you've also been told about the finite life of CF rifle barrels.

I think you need to understand your market more than you need to understand the technical issues.

Here are some fundamental questions for you:
1. How much comparative analysis/benchmarking have you done of the current top dogs in the market?
2. What does that analysis show as far as gaps that need to be filled? Hint: accuracy and resolution aren't it.
3. What kind of user feedback have you sought and received? Hint: asking leading questions (like this thread) isn't how it's done.
4. What does the user feedback tell you to do? What pains do you need to alleviate for your customers?

When it comes to business it doesn't matter how good of an engineer you are if the problem you solve is one that no one but you cares about.

 

[fe7565]

I think you are losing sight that I am coming to you guys for suggestions and recommendations and not to challenge you. I have airguns. I shot firearms when I was in the military. And I was in the AF, so you know how much shooting we do?

I am not here for business research, nor to gain customers. It's a hobby, but I want to get it right. An added benefit would be if it can be used as a commercially viable product, but looking at the potential time, energy and resources invested it is too early to even consider at this point. I am still building the prototype for the proof of concept. I am not even looking yet into FCC or EC certification or any state/federal laws, etc

I am here to solicit technical advice to incorporate any "low hanging" design changes into what I am building. My main objective is airguns. I know airguns. Firearms, not that much. If I would pretend to know it all, I would not be coming here, and I would not be asking you any probing questions. I came here to be educated and not to be lectured to.

If you read through my thread, you can see that I brought up "what ifs"and I conceded when I was explained why it will not work. I eliminated already several of my original ideas that I brought up once they were proven not feasible by the other commenters who cared to take their time to respond. It's your world. I conceded that placing it on the barrel in a permanent way is not feasible because barrels get replaced often. I was absolutely not aware of that, and I said so. I was no aware that hunters without threads still have a need for chrono until it was pointed out. I also explained from the very get go that my current design as it is (carbon fiber) would not stand up to any firearm air pressure.

What I still did not get a serious reply to is my original question: what velocity range would a firearm chrono be useful and what accuracy and resolution would you expect? The Labradar is excellent with a 0.1% accuracy. That is +/- 2fps with a 4,000fps bullet. Is that the minimum acceptable accuracy? What about the displayed resolution? 1 fps?

Why don't you grab a few rounds Gunny and go shoot some..come back...and then we continue! By the way, you are welcome anytime in my world, on the AGN forum!

 

[Mudmarine]

The lab radar specs are perfectly acceptable for rifle usage. One could argue that making ammo with low ES e.g.under 10 (extreme spread) and SD (standard deviation) is the limiting factor, not the current state of the art.

A chrono that is accurate out to 4000fps would probably cover more than 99% of small arms applications.

Is your project opensource by any chance?

 

[1moaoff]

Labradar is .1%. Dont think anybody cares about much more then that. Sure it would be nice, but best thing about labradar is no POI shift..

No po shift on MS if mointed to the chassis

 

[308pirate]

I think you are losing sight that I am coming to you guys for suggestions and recommendations and not to challenge you. I have airguns. I shot firearms when I was in the military. And I was in the AF, so you know how much shooting we do?

I am not here for business research, nor to gain customers. It's a hobby, but I want to get it right. An added benefit would be if it can be used as a commercially viable product, but looking at the potential time, energy and resources invested it is too early to even consider at this point. I am still building the prototype for the proof of concept. I am not even looking yet into FCC or EC certification or any state/federal laws, etc

I am here to solicit technical advice to incorporate any "low hanging" design changes into what I am building. My main objective is airguns. I know airguns. Firearms, not that much. If I would pretend to know it all, I would not be coming here, and I would not be asking you any probing questions. I came here to be educated and not to be lectured to.

If you read through my thread, you can see that I brought up "what ifs"and I conceded when I was explained why it will not work. I eliminated already several of my original ideas that I brought up once they were proven not feasible by the other commenters who cared to take their time to respond. It's your world. I conceded that placing it on the barrel in a permanent way is not feasible because barrels get replaced often. I was absolutely not aware of that, and I said so. I was no aware that hunters without threads still have a need for chrono until it was pointed out. I also explained from the very get go that my current design as it is (carbon fiber) would not stand up to any firearm air pressure.

What I still did not get a serious reply to is my original question: what velocity range would a firearm chrono be useful and what accuracy and resolution would you expect? The Labradar is excellent with a 0.1% accuracy. That is +/- 2fps with a 4,000fps bullet. Is that the minimum acceptable accuracy? What about the displayed resolution? 1 fps?

Why don't you grab a few rounds Gunny and go shoot some..come back...and then we continue! By the way, you are welcome anytime in my world, on the AGN forum!

Now that you've explained more, I have nothing further to add and zero interest in your venture.

But thanks for asking.

OBTW, I shoot plenty with a USPSA match every weekend and at least one range session and 3 - 4 dry fire sessions every week. My long range rifle is having some barrel work done and once I pick it up next week I'll be putting in more mileage on it.

 

[Baron23]

Ow wait a second. I may be wrong (not having the best day) but you threw some shade at Labradar for only going out to 100 yds but you are planning to make a muzzle mounted chrono that will go out....nowhere past muzzle velocity?

Almost everybody here is more expert than I, but equipped w good muzzle velocity you can go into a ballistics calculator and get a Try DOPE card out to..whatever you want (within reason).

Then you shoot. Determine actual DOPE, and use that to true your calculator. Also see Marc’s write up of weaponized math which, if I’m correct, let’s you interpolated data for distances between those at which you shot.

 

[308pirate]

Ow wait a second. I may be wrong (not having the best day) but you threw some shade at Labradar for only going out to 100 yds but you are planning to make a muzzle mounted chrono that will go out....nowhere past muzzle velocity?

Almost everybody here is more expert than I, but equipped w good muzzle velocity you can go into a ballistics calculator and get a Try DOPE card out to..whatever you want (within reason).

Then you shoot. Determine actual DOPE, and use that to true your calculator. Also see Marc’s write up of weaponized math which, if I’m correct, let’s you interpolated data for distances between those at which you shot.

He's not really interested in how we use chronos or anything else. He's only interested in the answers to a pair of technical questions that most of us don't really care about because the current offerings have that covered in spades.

He just made a bunch of assumptions about firearm users, almost all incorrect. And when advised to understand what we really want and need out of a chronograph he doubles down on the technical aspects.

Being an engineer who successfully made the jump to understanding customers and crafting solutions that solve their problems, this is a train wreck I've witnessed before: "I have the best answer to the question that nobody asked"