I have two chronographs. I'll leave the brands out to keep biases to a minimum for now. The reason for getting a second was simply to get more readings in less than perfect lighting. The new one is great for getting readings. Very rarely misses a shot reading. I did notice that all my loads seemed a bit slower though. Same rifle, same powder, etc. In fact many were loaded the same day awhile back and thus have been shot through both chronos. So, today I set them up and shot my bow through them. They were set up such that one was inside the other to make the readings the same. The new one read slower every time. I averaged it to 1.5% slower. For rounds shooting 2700ish that would equate to ~38FPS. That is in the ballpark of what I was seeing.

Is that typical of chronographs?

Are you sure the problem is that one is reading slower and not that one is reading faster

It's all relative. I am certain that one is reading slower than the other and the other is reading faster than the other. No idea which is right.

With the same brand of rifle, same brass, same bullets, same powder, same primer the faster chrono readings very closely matche the loads published by JB in his article on loading for the 338 FED.

Buy a brick of x500 22RF target ammunition, use it to 'calibrate' the chronograph before each session by firing say 5-10 shots. That way the 22RF can be used as a reference for whether lighting conditions on that particular day were conducive to high or low readings.
Cheers...
Con

+1

I like the .22 idea for understanding day-to-day variability. Now I just need to find a way to determine which is closer to correct.

Trying to get a grip on this but if I have it right you have 2 clocks on ones about 1.5% slower than the other and it's doing that consistently right? Thinking if it's that big a deal that you must be into shooting tween 500-1K a lot?

Gotta ask, what is it about the 30-40 fps diff tween the two that's so important to you?

Shoot the rig to those long ranges and make your notes and roll on.

Best of luck to ya

Dober

Definitely not suggesting it's a big deal. Really, it might make a half a bullet width difference at 100-200 yds! More of an annoyance. Really just more curious if there is an easy way to resolve which is correct. If I could shoot at 500 or beyond easily (East coast sucks in that regard) I would probably care less about a chrono. Reality trumps a chrono every time.

True that it does.

I get intrigued by the day to day diffs on how clocks can read. I think, mainly due to different light conditions?

Dober

Been my experience. I figure you really can't trust chrono results or group size unless you have repeated the process a half dozen times.

Yes, lighting is the most important parameter for proper skysreen function. It does make the design of skyscreens a challenge.

We regard the use of a .22 (or even an air rifle or BB gun) to be a reasonable test of chronograph function. We do not consider it to be a reliable calibration.

If you want a definitive test of accuracy, you will be testing chronograph "pairs" from different makers. If the two units of a pair agree, you have a chance of accuracy. If the units don't agree, you know that at least one is wrong. It is a pain to set up six or eight chronographs to measure the velocity of each shot, but we know of no better way to do a test.

KenO

Thanks Ken. Has it been shown that sun angle changes readings? In other words, will a chrono consistently read differently when the sun is directly overhead vs. low in the sky. Assuming it gets readings of course.

Yeah, how come we can get fast or slow readings on certain days? And what about the screens, how important are they on bright or dark days?

Thx
Dober

Over cast days are the best for accurate chronograph readings

Buy a third chrono, shoot over all three and take an average.

I've read that before, but I don't understand how accuracy would be impacted.
I see how it could impact getting a reading, but if it gets a reading why would accuracy be changed?

The box has worked best for me in bright days. Still like overcast the best also but the box works on bright days.

The box? What is?

Lighting conditions do make a difference. With more diffuse light, such as you get when the sun is behind a cloud, the image of the bullet on the photosensor is not as sharply defined, and that does affect the point at which the electronics think the bullet passed.

The other thing that makes a difference is the height of the screens. If I put the extenders on my Chrony, it drops the readings about 25 FPS.

Most people seem to like to do their chronographing on a cloudy day. I guess I'm the one that's different. I do all my chronographing during the middle part of the day, with diffusers in place, on days when the sun is distinct enough that I can see the shadow of the tripod. Since barrel temperature is a major factor, I fairly often strap a thermocouple to the barrel, just forward of the receiver.

The other thing to be aware of is that Ken Oehler says that there is about 1/8" uncertainty in the effective distance between the photosensors. I suppose this relates to getting the photocell and the lenses perfectly square with the frame of the chronograph.

I have no trouble at all replicating results from day to day.

This is the innards of a sensor from a CED M2 chrono:



The sensor is looking for the flicker of a shadow (green line), which tells it a bullet just whizzed past. If the sun is low, its light can bounce off the sides (pink line), then strike the sensor. The passing bullet doesn't interfere with this light in the least, which makes it all the harder for the sensor to detect the shadow.

Provided you have a truly accurate BC (and what many manufacturers publish is not truly accurate), you can use something like JBM's ballistic calculator (online) to "reverse-engineer" MV from BC, zero range and bullet drop at range (preferably at least 2x the zero range). That should give you a better idea of which is the more nearly accurate.

Using an IR light source solves about 90% of all consumer chrono problems.

Having proper light is essential to chronograph function. The challenge is to design the skyscreens to use available light to your advantage.

We won't get into the design and operation of skyscreens. We are talking about trying to measure the effectiveness of the skyscreen/chronograph system. To measure the effectiveness of the skyscreens, we consider that the second velocity reading on the same shot is essential. It is just about in the same league as trying to measure rifle accuracy by firing one-shot groups on various targets at various ranges. When you fire a two-shot group on a single target you at least get an indication of where the third shot will fall. If the first two shots are close together, you then expect the third shot to hit nearby. If the first two shots are widely separated, you have no idea where the third shot will hit. If you can make two chronographs read very similar velocities on a single shot, you can reasonably assume that both chronographs are accurate. (We'll assume that you've eliminated all the gross error sources such as screen spacing, alignment, oscillator frequency, timer resolution, totally inappropriate light, et cetera.)

KenO

Curious what you are running. I bought a prochrono digital to replace the shooting chrony f1 and putting them in front of thr other, 3 diff rifles 2500-3000 fps, the prochrono reads consitantly 50fps slower.

One of the reasons I like my Oehler is because I am always shooting over two chronographs.

Is the ultimate solution to go back to contact screens?

XL5---

The only chronograph I've taken apart is the Shooting Chrony. It had cylindrical lenses in the light path. From the picture of the CED, it appears that their design does not use them. Am I seeing correctly? Does the photo sensor have its own built-in lens?

It is a Prochrono that reads slower (~40 FPS for 2600-2700).

The most absolute and easiest and not to mention least expensive method is to just NOT use chronographs and trust the data in the loading manual. I'm sure chronographs can be of much value but I have handloaded for well over 50 years and hunted with those loads here and in Africa on many species up to and including Elephant. In all those years and rounds I have never had a handload fail to fire and I have never lost a game animal due to anything other than poor shot placement. I'm unsure as to how a chronograph would have made my pleasure any greater,my rifle more accurate or hunting success any better. As I stated I'm sure for those really concerned with data they are invaluable.

In my case i was working up loads for a wildcat based on measured case capacity. A chrono was pretty helpful even if it was +/- 50 fps.

Or perhaps everyone may decide to buy one so that they can talk about any differences between their handloads and the ones published in books.

Owning a chronograph isn't about accuracy or success. It satisfies one's curiosity. You obviously do not wonder about that, but others do.

Equipment is there to be used or ignored as desired, so I understand your post.

For example, I ignore Remington bolts. I have not had a failure to fire or lost game because I ignored the Model 700.

I chrono'ed my 338 Laupa on a bright sunny day with only the diffusers in use, with no additional shade and got 2820 FPS average velocity. My drop were low at 972 yards. I recohrono'ed on an over cast day and I got 2791 FPS avereag velocity and my drop were correct with exbal ballistic software and not low. The difference of only 29 FPS is only important in predicting trajectory at long distance and not so much at 5 to 6 hundred yards IME


I was useing an Oehler 35 in both instances

There are some fairly simple things you can do to limit the damage from unusual lighting conditions, without resorting to buying IR sky screens. When the sun is low on the horizon, most camera tripods have an articulating head, which will let you tilt the chrono so the sun strikes it from close to the same angle as it would if it were directly overhead.

I cut out a small section from an old translucent shower curtain I was throwing out, which I keep in my chrono box along with a couple of black steel binder clips. If my gun-target line won't let me tilt the chrono the right way, sometimes I can clip that piece of shower curtain on the supports for my sky screen so it shades the sensors.

The critical element in loading for long range accuracy is standard deviation of muzzle velocity. If you roll your own, the easiest way to monitor SD -- and the best way to QC your loads -- is to chronograph them. So owning a chrono is about accuracy. And success, provided you define 'success' as small groups at long range. I shoot over a chrono almost every time I shoot at paper, not out of curiosity, but to QC my work by monitoring my loads' SDs.

But my use for it evolved to that. My original purpose for buying one was so I could use the Optimum Barrel Time method of load development, which requires the knowing of MV.

I also shoot coated bullets, not Moly but tungsten (WS2) and boron (hBN), which do the same thing as Moly, only better. But the slickness of coated bullets generates lower chamber pressures, which leaves you to your own devices for fixing a max charge weight because the manufacturer's load data for naked bullets doesn't strictly apply. So I use MV in addition to my pressure reads after the shot is fired for establishing a max safe coated bullet charge weight.

With a chrono I can trust, and with predictably low SDs, I can do my own BC testing, in case I'm using bullets from a manufacturer who based their "predicted" BC on computer modeling instead of range test data. And with two trusted chronos, I don't even need the low SDs.

So, no, it's not just about curiosity. If you bought one just for bragging rights, that's hardly the chrono's fault.


The M2 has two external lenses. The first is visible in the 'floor' immediately above the two bosses with the screw holes. The other should have been in the slot visible in the floor immediately below those bosses. Except when I separated the halves, the smaller, lower lens stayed lodged in the opposite shell. I was taking it apart to dry it out after it got drowned in a thunderstorm, and taking pictures was an afterthought. And I had reassembled it before I'd noticed the goof and haven't yet found the motivation to take it apart again just so I can shoot more photos.



It completely recovered from the flooding, BTW.

Exactly.......

That's your personal experience which I do not believe is shared by the majority of users. Most chrono owners do not shoot long range or attempt to develop and fine tune their loads for long range hunting or competition.

You haven't changed my view of chronos. I'm convinced that it's not about accuracy or success. I see their use as a way to satisfy personal curiosity. Most buy Chrony or Pact models which would not be at the top of anyone's list if absolute precision was required. I'd be inclined to buy one of Dr. Oehler's products if I wanted performance.

As far as that goes, if the shots are out by 30 or 40 fps, I doubt that it matters too much to the great unwashed. They're happy to see something on the display about their loads.

Bear in mind that I am the board's resident stats geek...

A lot of people just aren't curious about the technical side of the hobby. I have absolutely no quarrel with them. There is a lot to be said for keeping it simple, jamming half a box of Super X in your jacket along with some power bars, and a half-frozen milk jug of water, and slipping out of the house early enough to be in place before daylight.

To some of us, this hobby is a grand engineering experiment.

To us, a chronograph is an extremely useful instrument, probably the most accurate and repeatable instrument we can access.

If your loads are exceeding "book" velocity, they are almost surely exceeding "book" pressure. That's a good safety application.

If you are developing longer range loads, it's good to know your MV so you can set your elevation at 100 yards so that it will be close farther on out. That's a time saver.

If you're doing benchrest level shooting, a chronograph is a big help in developing process consistency. That's a competitive advantage.

If all I shot was a 30-06, 270, or other common chambering, and if my only need was to be ready to hunt, I don't think I'd need one. But for the things I like to do, it's a useful tool.

The tone and conceiceness of the last two posts do not stop me from having to wonder what we will quarrel over next?

Ammo wallets - do you use one or don't you.

Which, when, how. And why the others have lost their marbles.

I am one of the two posts and answered XL15. In short, I do not agree with him, but I hardly see what I posted as anything insulting or negative.

Would you have preferred that I called his views idiotic? That's how people start silly arguments.

...the great unwashed..., hardly a "neutral" adjective, but, since I see Denton's point(s) and concur, I shall leave it at that.

Spot on, it is the "unwashed" that doesn't get this

THANKS JWP for going to the trouble of limiting XLs quote......

so I didn't have to......

I do agree in GENERAl. However I've observed 'exceptions to the rule' a little more often than I expected.

I look for low SD and ES BUT I've also had 'better than average' groups from loads with higher SD-ES. Curious to me, but have been unable to explain to my own satisfaction how that happens.

I would be surprised it you or others have not experienced the same.

OTOH I have no place to hunt extreme ranges. 400yds is about maximum area for seeing and shooting. Therefore I've been satisfied with loads from 1/2-1" groups (outside-outside) not center-center. I'm sure y'all understand that diff.

On another subject, I rarely find myself on the same page as Mr Redgwell.

I dunno - I wash regularly and I get it.

I hate anything that is too technical.....this a character defect.

But I have to admit that handloading without a chronograph is like running a Porsche blindfolded....it may be fun, but is sort of irrelevant from the standpoint of learning anything.

I think that we agree here. My belief is that the majority of users fall within this group.



I believe people like yourself who use chronos to this extent are the minority. That would be long range loads, bullet drop calcs and benchrest shooting.

I'm not convinced that your average Joe uses it for anything other than MV and hoping perhaps for single digit SDs.

I thought I had a good loas with 130 gn balictic tips untill I ran them across my chronograph, they did not show any signs of high pressure, they were with in book specs but the 3240 fps said I was sleeping in the street.

Before getting a chrono, I used to fire factory ammo (if available) in the rifle, measure factory pressure rings, and work up loads in the same cases, monitoring the pressure ring measurements to judge pressures relative to factory loads.

Then after breaking down & buying a chrono, I found that one box of factory .25-06 ammo I'd used as a reference was about 300 fps shy of published velocity. That discovery was an eye-opener, that my reference point was no good.

How many of those "better than average"/"higher SD" groups were at 1000 yards?

I'd wager NONE

You are both correct. I stated that in the earlier post. Since I have NO long range opportunities, I haven't gone to that extreme.

However, depending on caliber of bullet, 1/2" outside-outside is pretty darn good.

Yes, 1/2" outside to outside is good, but with a wide estreme spread at distance verticle dispersion rears it's ugly head

^ This.

After loading for a lot of years without a chronograph, in 1971 I designed and built one. Cumbersome as it was to use it still taught me that sometimes the books and the rifles could both be right and the numbers could be wrong. It also taught me that any one of the three could be right and the others wrong.

I never work up loads without the chronograph. I don't care if it's a little high or a little low. Doesn't matter. as long as it stays more or less within a small (< 5%) range, it will tell me if I did something unexpected in the load. If it and the load are where I expect them to be, things are good. If something is wrong having the chronograph reading is a powerful tool to sort it out with.

I have never bothered about SD or ES. The holes n the paper tell me what I need to know there.

Just one example from yrs ago. I bought a Rem 700 300 WM in Hammond La. The FIRST group I shot (handloads) w/180 gr bullets - 4, 30 cal.bullets were INSIDE of 3/4". That's the dia. of a nickel.
That's OUTSIDE-OUTSIDE. A nickel completely COVERED the 4 holes. That more than good enough accuracy for 400yds +.

I took the target to the SG store where I got the gun and the guy said, "I didn't know a 300 would shoot that good."

While the utility of accurate velocity on trajectory calculations is useful, the main reason for measuring bullet speed is to get a closer idea of pressure. When velocity gets to the book value for a particular load, one can then get a reasonable idea that pressure matches that in the published load.

The business of measuring case heads is pretty weak, as is doping pressure by sticky bolts or flattened primers. The chrono helps to get to safe max loads, and I think that's its main purpose (for a handloader, anyhow).

On the contrary - concise and polite.

Lest someone miss the trivial aspect of the point -

chronos - either one does or one does not - my post.

Not many publish pressure... and there are good reasons for that.

I'm looking at my shelf for handloading books right now: There's Hornady, Nosler, Barnes, Speer and Sierra that have NO pressure data in them.

Hodgdon has data in CUP, which is practically useless; Lyman the same, but with some in psi. Accurate Powders now publishes in psi.

Then, some of the published loads that have no pressure data except a generic statement like: "These loads did not exceed the maximum pressure by SAAMI" are all over the map.... I checked MANY of them where a tech person was willing to give the actual data.

Bob

www.bigbores.ca

They used to publish those figures, but don't any longer because the results are only good for that rifle/test barrel.

Using velocity as an indicator of relative pressure has some merit. It's best to start with known loads and actual pressures from a particular firearm, but velocity spikes can indicate high or over pressures. The reverse can be true as well. Lower velocities can suggest pressure drops.

CZ - Our resident MATHGENIUS, Denton Bramwell, has published an

equation to convert CUP to PSI. I found it when I googled CUP - PSI.

HIS equations is: CUP x 1.516, minus 17902.


His info is helpful and I'm trying to be.

::

...with the caveat that the formula only works for rifle cartridges, and only above about 35K CUP.

Thnx - I didn't notice that in either of the places I read it.

I think it fits in this discussion.

Thanks Again

Jerry

Denton and I have hashed this around before, but I'd add the caveat that his formula describes the relationship between maximum average pressure (SAAMI conformal piezo) and maximum average pressure (SAAMI CUP) as specified for a number of cartridges. The exact relationship is very dependent on actual cartridge and load tested.

Ken

A man with one watch, always knows what time it is.

A man with two watches is never certain.

That criteria is exactly why I don't have all faith in 'published pressure' figures. I believe those ARE the pressures, whoever got in THEIR loads and THEIR guns/blls.

We should not and can not expect them to be exactly the same in OUR guns with our components.


On another note: MR Oehler, I want to say THANK YOU again for your contributions to us professional AMATEURS in the shooting sports. I've enjoyed my O - 33 for a lot of years. I'm seriously considering buying a 35. I'm beginning to suspect its age is catching up to it.

Very true relative to his world..... :-)

On a good day my bargain-basement chronys would give me a reading 2 out of 3 shots. On bad days I was lucky to get a reading on 1 out of 3 rounds sent downrange over the sensors.

Last year I bit the bullet and purchased an Oehler 35P. I haven't missed a reading since.

For anybody interested here is a new model that seems to be getting some pretty solid reviews.

www.magnetospeed.com

Ken did a beautiful experiment a while back, with two strain gauges and two piezoelectric transducers on a single barrel. He'll publish his results in his own good time.

There was one result from his data that left me seriously gobsmacked: If you could build a pressure measurement system with zero random error (as opposed to systematic errors such as setting up the equipment wrong or using a wrong number in a formula) it would do practically nothing to improve our ability to get a more precise estimate of pressure. The reason is that cartridge to cartridge variation (in a supposedly identical lot) is a greater factor that the random error in either the strain gauge or the piezoelectric system. Random errors do not add linearly, and the largest single source of error almost completely determines the total error.

So Ken is exactly right. Predicting the typical PSI of a load from a single CUP measurement is iffy business because there is a lot of cartridge to cartridge variation. The conversion I worked out converts the specification from one system to the other. Fortunately, that answers the question that is most often asked: If my upper spec is 50 KCUP, what would my spec be in KPSI?

Now, to the topic of this thread, predicting the mean muzzle velocity of a batch of ammunition from a small sample has exactly the same problem. By far the dominant source of random error (as opposed to systematic errors like lighting issues or photosensor placement) is cartridge to cartridge variation. The only way to get a true measure of the mean MV of a batch of ammunition is to shoot and measure it all. If you're willing to settle for a good estimate, 5-10 cartridges generally give an adequate approximation.

It is unrealistic to expect the same reading over and over again from a chronograph. And the problem probably has nothing to do with the instrument. If you shoot a sample on one day, and come back the next day to replicate your test, you practically always will get a little bit different number just because of the differences in cartridges.

With only a little work, you can produce ammunition with an MV SD of about 20 FPS. A sample of 4 cartridges will give you a 95% Confidence Interval of plus and minus 2 x 20/(square root 4) = 20 FPS. So some days you'll be plus 20 FPS and some days you'll be minus 20 FPS, and all it means is that your cartridges were not identical. 5% of the time your means will be outside even those limits. That doesn't mean the chronograph isn't doing its job correctly.

Thanks for posting this. It looks like an easier way to set up. I imagine that it will raise a few eyebrows at the range as well, the first time it is used.

Thanks Mr B - These are very interesting points and maybe the most important?

It's funny to me, to get the 'mean MV' we need to shoot ALL of it. That certainly would work.

denton,

Wouldn't an n of 30 adequately represent that single lot of ammunition you reloaded (assuming the total population is 100 or more rounds)?

I think most people don't realize that once they switch one component the statistical analysis (S, ES & mean velocity) they performed previously has to be repeated with that new component (I.e., different powder lot#, different bullet lot, newly formed brass) loaded with the other components from run #1.

A very simple observation from a very simple person: when we shoot from south to north, our Chrony is very good about catching every shot and doing so with (as near as we can figure - Winchester .22s that are advertised at 1280 fps went 1280-1286) acceptable accuracy. When we shoot west to east, we experience all sort of interesting events such as missed shots, shots with the same load that vary a great deal, and overall readings that tend to be significantly higher than those that grade out well against the standard of the .22 readings when shot to the north. Utilizing what is admittedly the least scientific brain imaginable, it looks like when shooting north, the angle of light hitting both sensors is the same, while when shooting east, the angle of light hitting the sensors is different.

When you learn basic statistics, you learn to do the Z Test, and that requires about 30 samples in order to work right.

Over and over again in our Six Sigma classes, we get people that remember just that one thing about the Z Test, and that think it applies to all of statistics. We've come to expect to hear that at least once per class!

Actually, since about 1925 or so, when Gossett invented the T Test and Fischer invented ANOVA, the magic of having 30 samples has disappeared... unless you want to resurrect the old Z Test.

I think that a better answer is that the number of samples you need depends on how much precision you are willing to pay for. More samples = better precision.

Of course, getting a good estimate of SD requires more samples than getting a good estimate of a mean.

Aha! A nit that needs picking.

• "Student". 1908. The probable error of a mean. Biometrika 6:1-25.

Original paper (pdf): http://www.york.ac.uk/depts/maths/histstat/student.pdf

The 1925 date for Fisher is OK; that's when his book on anova first appeared. He anticipated it in a paper published in 1918.
--Bob

LOL... good catch!

From here, 1908 looks pretty close to 1925.

That is what I learned while hunting with my 280 vs. running it over a chrono. All the years I spent chasing the ultimate fast load were instantly disproved when I saw that 280 load read 2820 fps. I had to reflect upon all the spectacular (I thought) kills this commercial round made at 2820 fps.

Gee, I thought the animals would laugh at me if I weren't running everything at least 3200 fps.

There are several on this board, present & past, that simply cannot abide anyone disagreeing with them. I could name them but I won't.

I have the ability to entertain a thought without embracing it. I also have the ability to allow you to speak your mind as you are entitled to do so, even if I disagree.

You appear to be of the same mind.

Amen !!

Looks like my chrono use will be revolutionized once again.

I have an old fashioned chronograph that came out before Oehler and just about everything else: Step 1- Load slightly under maximum pressure and tweek load and rifle as necessary to obtain acceptable accuracy (usually the first bullet and powder tried if sense is used in their selection); Step 2- Practice shooting at 100, 200, 300, and however many yards you plan to shoot when it really counts; Step 3- The final "velocity" figures are counted by game placed in the freezer, scores on target, trophies on the mantle, and other indicators of success. It's absolutely foolproof and gives 100% accurate results every time.

A chronograph is a tool and as with most tools its usefulness depends on the knowledge and skill of the person using it. I can tell a lot about a load I'm working up by seeing how velocity changes with small changes in powder weight, seating depth, and primer; things you'll never spot shooting paper. Of course, this is all meaningless to those who shoot factory ammo or blindly follow reloading manual recipes.

Very true, MacLorry, and well said.