If I'm reloading within the limits of published manuals, why would I need a chrono? Seems all I need is to tune my gun to the most accurate load for me and be done with it. I'm not interested in the slightest in hot rod loads for handgun or levergun.

Because you are 'cluelss' without one.:confused:
I got one about 20 years ago and it was sure an eye opener. Each gun is different. I had a friend who had a 300Wby and he thought it was a laser, flat and hit hard. He swore by his loads. When I clocked them they did 2700 fps, my 06 was clocking 2790 fps. Sure took the wind out of his sails. You will have alot more fun working up loads for ANY gun when you can clock them!

Maybe you don't "need" a chrono, given your contentment with the way loads work for you. They are nice to have....another tool in the arts of reloading and shooting. I use mine only occasionally to check a load that has aroused my curiosity. It's, also, a way to verify that what the loading manual says is true for your guns. Using a chrono is a way of knowing more about what you are doing. "Should" you buy one? Does anyone really "need" one? Can't hurt.
Pete

I have been considering a chrono...any good recommendations?

I also am seriously considering buying one. I'm rather anal (probably a good trait for a hand loader) and I spend a lot of time at the computer playing with ballistics software, comparing different loads and their trajectory, Kinetic energy, etc. Without a chrono to clock the loads, I'm only guessing.

On the next trip to the range, I'm going to adjust my scope so I hit zero at 175 yards, then shoot a few groups at 50, 100, 150, and 200 yards. Then I'll input the variables into the ballistics software, and keep adjusting the input velocity until the trajectory charts most closely match my observed target trajectory.

Why do all this?

1) So I'll have a good idea how much velocity I loose with the short 16.5" barrel on my Ruger Compact
2) So I can calculate the theoretical differences of a softer-kicking 120 grain slug to the 140 gr slug I'm currently using, before I invest time and money developing another load.
3) KNow how low I can load a round for my grandkids to use, without making it too slow to have the desired energy for effective kills on deer
4) I need an excuse to spend more time at the range.

Why buy a chrono? Because if you have loads of extra time on your hands, that will take it and keep you off the streets!:p

I have a Chrony, and it's temperamental, especially in bright sunlight. You get to do a lot more shooting though, because you want that data, and when you get 'error' or 'no read', you have to shoot more to get the data you want!

I'm being overly critical, but seems chrono's can be like scopes or binocs....spend what you can to get a good one. Mine has good days and bad days, and when trying to develop loads with the right mix of velocity and accuracy, you can get accuracy without the chrono, but velocity....if you get no-reads or errors, you are left guessing in the +/-200 fps range based on load manuals with typical bottleneck cartridges.

A chronometer can help you develop more accurate loads. Consistent velocities tend to produce better accuracy. If your chronometer shows wide velocity variations, that is a symptom that suggests there are things you can do to improve the consistency -- and therefore accuracy -- of your load.

A chronometer is also important if you want to develop a ballistic table for your favorite load in your gun, so you'll know exactly how much the bullet will drop at various ranges.

A chronograph isn't an absolutely necessity for a reloader, but it does take the wonderment out of the reloading process.

I'm on my 4th chronograph at this time. Took a while to find one that seemed to give consistent reads in all atmospheric conditions. Not made for the non-commercial shooters anymore, so will mention my backup is a Pact PC2, the older model of today's offering.

Since tweaking the loads for all the centerfires for best accuracy within the boundaries of safe powder levels, the chrono hardly ever makes it out of the truck when getting to the range anymore. Sometimes the groupings will get squirrely and it gets set up to see if it is the loads, weather conditions or me. Usually, its me.

So, no - you don't have to really have one if you develop loads you're satisfied with and check out the trajectory out at all possible hunting yardages. Sure is nice to verify just what's going on with the cartridges, though.

just because inquiring minds want to know!

:)

i would say the best reason to buy a chronograph is look at the current thread ' going above published data' in the Handloading Procedures and Practice's heading.
they are an important safety tool for load development.

Here's my chronograph spiel, once again.

If you are a reloader who assembles one box of deer-hunt ammo a year, stays absolutely within book data for loads and happily shoots to "minute of pieplate" accuracy, you do not need a chronograph of any kind.

If you are one of the vast bulk of reloaders who strive for a high degree of consistency, shoot hundreds to thousands of rounds a year, sometimes like to push at the edges of the envelope for velocity, or consider reloading as much of an entertaining hobby as the shooting, then you definitely need a chronograph. It need not be a Rolex-equivalent. One of the better Shooting Chrony models, a CED Millenium, PACT or similar models is more than enough. That said, the "tackle box syndrome" will apply: if you buy the bare minimum to fit your expected needs, you immediately discover new and expanded needs -revealed by that basic unit- that the unit cannot meet.

If you are a wildcatter, writer, or work with cartridges for which there is little or no puiblished data, you need the best chronograph you can find. Formerly, that was the Oehler 35P, now discontinued forever. (I am a good friend of Dr Ken Oehler, and you may trust me - he is out of the business.) I haven't reviewed chronographs, so I cannot make a recommendation here. Simply read the specifications and buy the best model you can find regardless of price. Or pounce on any 35P you find on an auction site.

Thanks for the thread, I will be getting one in the next while.

I would recommend the CED Millenium II. I have one and also an Oehler 35P. They track quite well. The CED has an optional IR screen available and if you shoot indoors or, like me, have range sessions that go on until dusk, it guarantees it will function without regard to external light conditions. I have not tested other brands except my Dad's old model Chrony, which has poor accuracy and consistency compared to the other two. If money is no object, the PVM-21 (http://www.neconos.com/details12.htm) is likely to be the Cadillac of currently available units.

As mentioned earlier, the chronograph can help with safety. One pressure sign is getting either no change in velocity or a decrease in velocity with increase in powder charge. You will probably find you set it up any time you shoot groups off the bench. It will then tell you how temperature and rate of fire affect your load's performance? It will tell you how fouling affects velocity? If you get a unit you are not afraid to shoot through at 100 yards, you can determine real ballistic coefficients with it. That is why I prefer the units that have the computer separated from the sky screens by wires, as the CED Milennium II does. It also has a large display you can see through a spotting scope pretty easily at 100 yards.

I have had one for about a year. It satisfied my curiosity about some oddball loads I shoot. Generally, I don't find it particularly useful. I shoot at least 300 days per year (constantly tinkering with loads) and I think I've set the chrony up maybe 5 times.

Here's what I use. I've used it in bright sunlight and in the evenings til it got to dark to shoot with great results. I had a gas check hit it from a 44 mag load when it was 15 feet from the muzzle (put it closer for gas checked pistol bullets) and when I sent it in Pro-Chrono fixed it for free, even though their stated policy is to charge half of the original cost to repair it. Good service good company and a great chrono for a hundred bucks at Cabela's.

http://i136.photobucket.com/albums/q172/faucettb/Preditor%20masters/Shooting%20accessories/Chrono300RUM180Factory.jpg

As far as the reason for having a chronograph, boy that's a tough one. I guess you could ask the same question about the reason to have an automatic transmission or air conditioning in a car or an indoor bathroom. Convenience is a big factor. If your loading without one you don't know what velocity your really shooting, your just guessing. For a hundred dollar bill you remove that guesswork and today that's hardly a tank of gass anymore.

I really like being able to see what my loads are doing out of each individual rifle I shoot, but then I shoot a bunch. If your a casual shooter or don't reload then it's certainly not necessary to kill game, but if reloading is a hobby as well as shooting then I've found it a great aid.

Sorry,I can't help with your selection of Chronograph.I'm lucky enough to own an Oehler,which is pretty much "idiot proof".
My first session with it,taught me the reason why i needed it.
I'm shooting a 30/40 Krag for many years.40 grains of IMR 3031 with a 150 grain bullet at 2650 FPS listed in several manuals.
The chrono only registered 2590 FPS.Acall to Texas assured me that my Chrono was Right;my manuals were all wrong.
Frank

I've had a chrony for about 7 years and it's the Pro Chrony Digital that Bob had pictured. IMO, it is the best chrony for the money out there...in the time I've had it, I've put thousands of rounds through it and have yet to have one fail to register. It's also about $100 at Midway (http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=852429&t=11082005) and check out the reviews, 32 of them so far and rated 5 star. Compare that to the others on there.

You may not think you "need" one, but once you get one, you'll wonder how you did without. One thing I learned is for years I had a load for our 270's for my brother and I that was devastating on deer. According to the book, it was supposed to be 2900+ fps. When I did get the chrony I found it was "only" doing about 2750 fps. I use it quite a bit when developing loads and it's definately helpful.

The reason you need a chronograph is related to Kragman's last post.

His manual and his chronograph were BOTH right. It's just that his rifle shoots differently than the one the lab guys used. And here's a secret: so will yours. It is rare to the point of being anomalous to find a rifle that delivers precisely the velocity that a load gave in the manual. I personally call anything within 100 fps to be a "match."

How do I know that? Tens of thousands of rounds over a chronograph.

How will you know that? Get a chronograph.

The reason you need a chronograph is related to Kragman's last post.


But what practical use is it knowing that your load is 60 fps less than what the book said? If it scratches the itch to know exactly what your rifle is doing then more power and god bless.

And that's the reason you DON'T need a chronograph.

See, the difference is that Kragman finds it important to measure and know what his loads are doing, but you don't.

There's plenty of room at the bench for all kinds of reloaders. As I outlined above, some of those reloaders will never need the instrument. Many (perhaps most) do.

An analogy might be with the guns. Lots of people are well-served and happy with entry-level rifles in common chamberings. Many of us can justify an upper-end gun, perhaps with some special tuning by a 'smith, and maybe in a less common chambering. And then there are the few who truly need a full-blown custom gun in a wildcat chambering.

See, the difference is that Kragman finds it important to measure and know what his loads are doing, but you don't.


But I do; accuracy is the measurement that most interests me. Careful shooting and measuring tells me this more than a chronograph will and I sure don't think that the odd 100 fps more or less makes much difference in the hunting field.

Just camping on so I can see the new banter. I'm considering a chrony myself, looking at the Millenium II. Still debating how much I would use it. Would I use it more than a K&M neck turn tool? That's my current debate.

I do agree there are good, affordable chronographs on the market that can satisfy some questions. But, maybe a strain guage, if similarly affordable, is actually more important to load development since it will likely disclose better pressure data for comparisons of variations in power charge or manufacturer. For example, most manuals indicate to me that Unique and Universal are almost interchangeable grain for grain. The chrony might say they differ by 25 fps in my gun, but the pressures could be more deferential. As I said, I don't hotrod loads now, so pushing the envelope is not my desire. I'm aware that some reloaders do want to do that, and a chrony in those circumstances probably is the most affordable way to monitor the safety issues for such loads.

One of the reasons I started this thread is my interest in lower velocity loads, not for cowboy action shooting, but for general purpose use adapting the bigger bullet less velocity thinking. Such as 300 grain bullets in.45LC or 330 grain bullets in .444. I'm not afraid to say that I simply don't have the constitution to stand up to hotrod loads. I've read alot about bigger and slower which leads me to believe that smaller charges actually have a greater tendency to cause blown guns than hotrod loads as long as hotrod is not way over limit like a double charge. I also believe that dead is dead. A bullet performing great at 2750 actual fps when reported to be 2900fps just emphasizes my belief. I'm also interested in using the same powder in my single action revolver as my levergun if I can do so within safe pressure limits.

But I do; accuracy is the measurement that most interests me. Careful shooting and measuring tells me this more than a chronograph will and I sure don't think that the odd 100 fps more or less makes much difference in the hunting field.

A chrono can can be a good way of know if you are within SAAMI presure limits.

I have a Shooting Chrony, which works pretty well. I've definitely found some interesting things with it.

Mine is the very basic model that was about $70. As Rocky mentioned, its the one that suits the vast amount of reloaders. I don't use it much, but its nice to have. I use it more for pistol loads than rifle loads.

A chrono can can be a good way of know if you are within SAAMI presure limits.

Limits (plural) infers a low-limit and a high-limit. I've only ever seen the high-limit data published. How do you establish a low-limit?

I have the least expensive Shooting Chrony. Quirks, yes when it is sunny you need to use the little plastic thingys to diffuse the bright sunlight. It has to be at least 10' away from the muzzle or the muzzle flash will affect the results (usually too high), Finally, I have discovered that you need to orient you shots over the center of the unit. Even though you have a sort of a triangle to shoot through, the more centered you are the fewer bad reads you will get. Taking these things into consideration - wonderful tool, very accurate, very reliable. I have to write my own numbers down and do my own statistics (my calculator has stats functions so I can do mean, and standard deviation, and I just subtract the slowest number from the fastest to get the extreme spread - that's all I use). The stats help evaluate my powder performance and load procedures. The lower my ES and SD are, the happier I am. If you have a large ES and a small SD, you probably had one bad load, but generally the load is going to perform well.

Now using this tool I can correctly evaluate handloads for my gun. Is my cast bullet going too fast and in danger of leading the barrel? Is the load way too fast compared to published speeds (something wrong in my load process)? How much faster is my 26" cowboy barrel than my guide gun at 18" with the same bullets? Are the cartridge manufacturers stretching the facts a bit about their muzzle velocity? Am I going the right speed for my expanding bullets to open like they should? If I have the correct speed of my bullets, I can calculate tailored ballistics for my loads (I use a software program) so I know how much drop my bullet is going to have in the field tailored to My gun and handload.

How's that? :D

Forgive my sloppy writing, KenK. What I meant to say is that you aren't interested in the velocity you're getting. Most of us are interested in accuracy and group sizes (not the same thing) but those of us who also measure velocity know that load consistency can be directly related to group size. Knowing both is worthwhile.

But I absolutely agree that 100 fps in the field is meaningless - if you know that is IS only 100 fps.

One tidbit here. What often causes bad readings or no readings on a chronograph is not muzzle flash but muzzle blast; specifically, the supersonic shock wave of gas that passes the bullet after muzzle exit. That shock wave distorts light, and triggers the chronograph sensors. Naturally, the wave is faster than the bullet so the reading on that shot will be a false high. Setting the machine at least ten feet from the muzzle allows the wave to dissipate and slow enough that the bullet once again passes it into clean air.

I'll add that that muzzle blast on the base of the bullet also accelerates it an additional few feet per second after it exits the muzzle. For rifle bullets, that will drop back down to original muzzle velocity after it has traveled about 10 to 15 feet, so there is really no advantage to being up close anyway if muzzle velocity is what you want to know (and you do if you are running a comparison to internal ballistics software calculations). If the display is hard for you to read at those distances, toss a cheap pair of binoculars into your range box and focus them up close. That's another reason I like my computer on the end of cables rather than at the sky screens. I can have the readout on the bench when the screens are safely out in front.


Flashhole,

Lower limits might be determined by stability at lower velocity? I can't think of other compelling reasons offhand, unless the load is so light you are looking at detonation concerns? I suppose it might be argued that the velocity inconsistency introduced by having too much empty space in the case might create a lower limit for you?

This has been a great post! I went ahead and ordered the Pro Chrono Digital from Midway USA. It looks to be simple, small, and the best thing is that it runs off of one 9 volt battery. I really dont see a need for one of those high end jobs (although it would be nice to have), but, if I can just get the velocity and standard of deviation, it would be very helpful for what I do! Thanks to all!!!!!

But what practical use is it knowing that your load is 60 fps less than what the book said? If it scratches the itch to know exactly what your rifle is doing then more power and god bless.

Ken
The difference was not 60 FPS,but 160 FPS.That is,in my mind,a signifigant difference.
Frank

Must be my math skills, but I read it as 60 fps, also. 2650 minus 2590 is um...yup, I still get 60.

Sorry,I can't help with your selection of Chronograph.I'm lucky enough to own an Oehler,which is pretty much "idiot proof".
My first session with it,taught me the reason why i needed it.
I'm shooting a 30/40 Krag for many years.40 grains of IMR 3031 with a 150 grain bullet at 2650 FPS listed in several manuals.
The chrono only registered 2590 FPS.Acall to Texas assured me that my Chrono was Right;my manuals were all wrong.
Frank

Have to report another dumb remark by me.
The actual velocity attained by that load was 2490;not 2590.
Time goes on
Frank

Yuppers, I thought there might be a typo in one or the other. No sweat. (Goodness knows we ALL make those!)

This is a great discussion. One thing I think I see emerging here is that a chronograph might slightly accelerate load development to the extent that one can acquire consistency information about a particular load without needing access to a long-range range and measuring group size at distance. However, I don't see how a chrono is very useful in determining maximum safe charges because of gun-to-gun, case-to-case, chrono-to-chrono, and other variations.

I don't have a chrono, but my brother does. Neither of us have a strain gauge. I can see some potential synergies if I had a strain gauge. Only downside is the 8 hours between us. :D

I will tell you one thing that happened when chronos got affordable....they let the wind out of the sails of many a wildcat! There was a lot of high side guess-to-mates with all the oddball wildcats.....and even some of the high flying loads offered today!
There is no way Ole' Dixie could operate without our chronos. Like Homer Powley used to say...burn the same amount of the same powder with the same weight/caliber bullet and get the same velocity within 5% in the same length barrel...no matter what shape the hull is! There is a lot of truth there.
A good chrono can give a great deal more info than just the velocity. With IMR powder...5% increase in powder = 5% increase in velocity = 10% increase in pressure. With that set of standards, there is a lot you can do with your loads...up or down. Most factory velocities (especially shotguns) the velocity might well be from a 30" pressure gun. Many loading manuals do not tell you what length the quoted velocity came from....we keep pushing them to state that fact. one well known slug company qouted a velocity of 1500+'/" (30" presure gun) that produced about 1225'/" from a standard 20" hasting barrel! The chrono found that fact quick!
Regards, James

Yeah, that would be a hindrance!

As a reloading writer, I'm almost required to have both a high-end chrono and a pressure system. There are two downsides to it.

First, it is an absolute royal pain in the keister to lug all that crappola to the range. Chronograph, light stands for the sensors, sandbags to anchor the light stands, the pressure system, the laptop to use the pressure system, the deep-cycle battery to keep the laptop running, plus the large cardboard box to keep the laptop dark enough to read the screen. Sheesh! That's before we even start to load the guns, the ammo, the range bag, the spotting scope, the front rest, the rear bags, the cleaning gear, the target stand..... If this were a safari, there'd be a line of porters with packs on their heads, I swear!

Second, It is axiomatic that the more questions you answer, the more questions you create. There's a Greek myth where every time the hero kills an enemy, three spring out of the sand to take the dead one's place. That sums up what it's like to own a chronograph - and trebly so for a pressure system. Every single answer creates a what if?, a Hmmm, but? and a Now wait just a second. And it never stops.

Blissful be the shooter who can gaze at the holes in a target and smile: "Good load!" The chronograph owner knows better, but not why. The chronograph plus pressure system owner knows better AND knows why - but also knows he doesn't understand why!

Have to report another dumb remark by me.
Frank

I'm glad this is not mandatory for forum participation.....I'd have pages of things to report on. :)

Even when using published loads, a chrony is nice for safety.

A while back I bought a can of Reloder7 and used some published data from a well known book for a nice moderate pressure load for my .45-70. I reached max velocity with about 4gr less powder than the max listed load. After finding this, I did some "research" on the web. Turns out that Alliant bought out Hercules, the powder had changed formulation, but retained the original name.

I probably wouldn't have found this out otherwise, and would have happily plinked away, thinking I was using a 20k cup load, when I was likely over 30k cup! I also didn't really want to hotrod my lever gun, but it turns out I was doing it by accident.

As far as I see it, my Chrony paid for itself with just this one particular load.

Chris.

"I will tell you one thing that happened when chronos got affordable....they let the wind out of the sails of many a wildcat!"
Absolutely!
If you suffer from the curse of curiosity, a chronograph will also show you that factory loads sometimes don't produce the velocity claimed for them- and in some cases to a degree that makes a significant difference.
Most of the arguments for using a chronograph have been well covered by others far more articulate than me. I will say, though, that if you shoot at long enough ranges to utilize a trajectory chart, as many varmint hunters, and some game hunters do, knowing the actual velocity of your load is absolutely mandatory.

Like Homer Powley used to say...burn the same amount of the same powder with the same weight/caliber bullet and get the same velocity within 5% in the same length barrel...no matter what shape the hull is! There is a lot of truth there...
<snip>
...A good chrono can give a great deal more info than just the velocity. With IMR powder...5% increase in powder = 5% increase in velocity = 10% increase in pressure...

This brings a question to mind about chrono measurements I've seen:
If we're seeing more than 5% (like maybe 15%?) difference from what a manual suggests we should see, and the manual provides firearm-used details such that we know it's not a barrel length issue, will brass and/or primer brand alone explain that much difference? Or is something else going on?

Lots of thing to factor in, but doubt if all things were equal that you should see that much difference. Remember - chrono's are just like any other mechanical device. Some read closer than others, some are more succeptible to atmospheric conditions than others. If you set it right off the end of the muzzle the readings will be skewed by muzzle blast. Mine get set approx. 15 feet out. There are programs to help calculate the true muzzle tip velocity from the couple fps lost setting that far out.

Now, rifle to rifle coming down the manufacturer's assembly line of the same caliber, length and boring will differ. Some will have tighter chambers and bores than others.

Your assembled loads can vary from day to day depending on ambient conditions and barrel heat. Yes, changing case types, powder types and primer types will all factor in the changes from published data. Loads assembled in January and logged will show a difference when shot in August and logged.

My chrono's are used in an aid to determine the best loads both in accuracy and in consistent velocities (as near as possible) within the parameters that are personally established. The published recommendations are used as a guide to keep me within those parameters and I try not to violate the maximums listed in the most trusted of the manuals - namely, the Lyman.

First, I have NEVER seen a 15% error in velocity when using the same components in the same cartridge. But if I did, I'd suspect something was grievously wrong with something!

Given a nominal 2800 fps, a 15% error would be 420 fps off - and that's simply beyond the pale of belief.

This brings a question to mind about chrono measurements I've seen:
If we're seeing more than 5% (like maybe 15%?) difference from what a manual suggests we should see, and the manual provides firearm-used details such that we know it's not a barrel length issue, will brass and/or primer brand alone explain that much difference? Or is something else going on?

We did have one case here on the board where a fellow was getting 25% variation from a snubnose revolver. That very short barrel creates a special case where the powder, one shot to the next, can be burning right around its peak pressure when the bullet exits or may already be past it, depending on how well the ignition went and where the powder was in its ignition progress at the moment the bullet base exposed the barrel-cylinder gap. The revolver also often has multiple chamber sizes if its cylinder hasn't been reamed for accuracy, so it is part of the way toward being like shooting several different guns of the same chambering. The solution in the case of the snubby was to go with a very fast powder. That knocked about 8% off its peak velocity, IIRC, because you can't put a lot of Vihtavuori N310 in without creating excess pressure. But at least the result was much more consistent, given that the super quick powder was all burned long before the bullet got to the muzzle. That sort of extreme aside, Rocky is right that wide variation isn't normal.

I somehow missed hearing of Powley's 5% rule before. It strikes me as curious. Just moving a 43 grain load of IMR 3031 under a 150 grain bullet between the .308 and 30-06 gives a 10% velocity change in a 24" barrel. Maybe I misunderstand, and Powley meant that all the variations of chamber and barrel dimensions within a particular chambering would stay within 5% of the velocity average? That's easy to believe, and comports better with my own experience with the Garands. They varied a little more like 6% over a range of the guns shooting Lake City M72 ammo, but that's close enough to 5% to think it's not a bad rule of thumb.

First, I have NEVER seen a 15% error in velocity when using the same components in the same cartridge. But if I did, I'd suspect something was grievously wrong with something!

Given a nominal 2800 fps, a 15% error would be 420 fps off - and that's simply beyond the pale of belief.



The most that I have ever seen was 8% . Only once have seen that large of a variation .

Let me try to make sure we're all on the same page here:
I'm talking about as much as 15% difference between chrono'd velocity vs. what the manual said we should expect with that barrel length, bullet, and powder charge. The only variations would be case and/or primer brand.

It's not that big a thing any more because that gun's down the road for completely unrelated reasons, but it was certainly curious.

Great discussion. I have one contribution and one question.

Contribution: I have a Chrony Beta Master and it suits my purposes just fine. It has a remote read-out unit that can sit on the bench where I can see it easily. The cord of the read-out unit allows me to get the chrony about the same distance from the muzzle from session to session. I don't know the current price for the Beta Master but over the last 5 or 6 years I have felt it was worth the money for the extra info it provides me. So I have a chrony for safety (although I rarely push the limits) and for satisfying my curiosity.

Question: Assuming standard cartridges with standard components (no wildcat, odd-ball powders, etc.) can MV be interpreted to indicate relative pressure?

For instance, XYZ manual says that a certain MAX load (powder, bullet, brass, primer) yields 2700 fps and is within SAAMI pressure limits. If my load hits 2700 fps with 1.3 gr. LESS powder does that mean I am at MAX and/or in danger of exceeding SAAMI pressure limits?

Vice versa, if I go to 1.3 gr. MORE powder before I get 2700 fps does that mean my pressure is still okay?

I have not been using my chrony in this manner as I see no need to push the limit for my shooting and hunting uses. But this use seems to be implied by some.

Question: Assuming standard cartridges with standard components (no wildcat, odd-ball powders, etc.) can MV be interpreted to indicate relative pressure?

For instance, XYZ manual says that a certain MAX load (powder, bullet, brass, primer) yields 2700 fps and is within SAAMI pressure limits. If my load hits 2700 fps with 1.3 gr. LESS powder does that mean I am at MAX and/or in danger of exceeding SAAMI pressure limits?

Vice versa, if I go to 1.3 gr. MORE powder before I get 2700 fps does that mean my pressure is still okay?

No, no, and no. That is one of the two reasons the instructions that came with your chronograph will state explicitly not to use velocity matching to develop loads. There are too many other factors involved in the pressures you will reach. For example, a load that produces maximum pressure in the capacious Winchester .308 case can exceed SAAMI maximum pressures rather handily if you pack it into a Lake City case. The tighter Lake City case will need higher pressure to match the velocity produced in the larger case with any powder. In addition, there are chamber and bore dimension differences that can affect the velocity numbers that result from a certain powder and bullet combination in your individual gun. It should go without saying that when you are getting the same velocity from one charge of a fast powder and from another charge of a slower one that the slower powder is producing lower peak pressure. That's why slow powders are useful. Because manufacturers use non-canister grades of powder, you basically have no way to match their powder burn rate, and so matching a commercial load's velocity will almost never produce the same pressure in your chamber.

The second reason is that you have no way to assess the absolute accuracy of your chronograph. You are just trusting the manufacturer to have got it right. When you see the improved instruments and versions that come out every few years, you realize nobody's completely idiot proofed this business yet. RSI describes a German study using Doppler Radar to continuously measure bullet velocity while evaluating numerous chronograph brands, all done using constant artificial illumination. Even under that condition the only two that produced a consistent match (.3% or better) to the radar were the Oehler and CED. RSI doesn't give a date, but I infer this was done in the late 90's and products have continued to improve since then. My dad and I were at the range one afternoon when he had his older Chrony set up and I had my Oehler set up side by side. Using a Savage rifle of his firing a very consistent target load, his Chrony was reading about 2700 fps average, while the Oehler read the same load from his same gun averaging 2500 fps. With those kinds of errors possible, you can see why the manufacturers don't want you relying on their machines even as a indirect pressure indicators. That would be a law suit waiting to happen.

MZ5, maybe that addresses your question, also?

I'll directly answer MZ5. Yes, that's what I meant: a difference between your chronograph results and book results with the exact same load. And I have never seen more than about a 5% variation between the two. Seeing 15% difference (high OR low) would raise the hackles right off my neck.

Just as I thought and that is why I do not use my Chrony in that manner. I have had enough instruction in research and statistics to know that in almost any human endeavor we are dealing with many more variables than we ever realize or consider.

Thanks for the replies.

Nick, inaccuracy of the chrono would potentially address the issue we saw. Do you know: Is a chronograph's consistency usually any better than its accuracy? Are the two (accuracy & consistency) often related in any predictive way? With this question, I'm really wondering whether most of the chronos out there (since the Oehler is no longer in production) have any utility at all other than feel-good stuff?

With this question, I'm really wondering whether most of the chronos out there (since the Oehler is no longer in production) have any utility at all other than feel-good stuff?

Since I'm about the only one on this thread that has minimized a chronographs utility, I'll jump on this question.

My "Shooting Chrony" seems to be very accurate and consistant. When I first set it up I shot a couple of different 22 rimfire loads through it and the velocity measured by the chronograph was fairly well what I expected. This doesn't mean it's exactly right but I would wager it is very close.

I think this is a good idea anyway given todays component prices just to make sure you have everything lined up and plugged in and what not before you start shooting those expensive loads.

Actually, as they all use almost exactly the same circuitry, there should be very little difference in readings (assuming the components in those circuits are of equal quality - not necessarily a valid assumption). Unless I'm way off base, they all use a quartz oscillator timing circuit and they simply count quartz oscillations from "On" (bullet triggers first screen) to "Off" (bullet at second screen). The number of oscillations divided by the distance between screens is the velocity.

I'm no electronics wizard, but this isn't cutting edge stuff, either.

Not necessarily the same circuitry. You can sense light with PIN diodes, phototransistors and other devices. They have differences, particularly as to sensitivity and speed. The PVM-21 is the only unit on the market I know of built by a company that specializes in high speed electronic switching devices, and is likely very good. It also is the only commercial unit with a 16 MHz clock, so it divides time more finely.

The Oehler, despite its age, has long been known to have the most sensitive sky screens. The only drawback to them is getting too near a transmitter, which can flumox them.

I don't know what is currently in the unitized boxes, but I looked at the specs on Chrony's site once and they are claiming accuracy equal to the accuracy of their 4 MHz timebase as if the sensitivity, propogation delay and screen slot and circuit board alignment had no effect, but they do. Especially with photo transistors whose gain can vary substantially within a part number. It is perfectly possible to have uncalibrated circuits trigger at different percent shadow levels. I think a lot of them are now set up to trigger when the bullet base clears the screen for that reason.

The newer type CED Millenium II is the only unit I am aware of that actually adjusts the sensitivity of the sensors with changes in ambient light conditions to try to keep the performance constant. As I said, they keep evolving.

Consistency should be better than accuracy if the light conditions remain constant. That's always the caveat. Some units change readings if you just tilt them on their tripods a little. Avoid those.

Since I'm about the only one on this thread that has minimized a chronographs utility, I'll jump on this question.

My "Shooting Chrony" seems to be very accurate and consistant. When I first set it up I shot a couple of different 22 rimfire loads through it and the velocity measured by the chronograph was fairly well what I expected. This doesn't mean it's exactly right but I would wager it is very close.

I think this is a good idea anyway given todays component prices just to make sure you have everything lined up and plugged in and what not before you start shooting those expensive loads.

Being exactly correct is not a problem unless you are shooting long range (past 600 yaards) I recently chrongraphed loads for my 338 Lapua with the 300 grain SMK in bright sunlight and got a reading of 2820 FPS. Useing this velcoity my drops were low at 975 yards. I re-chronographed on an over cast day and got a reading of 2791 FPS and now everything is OK.
I also set up my Chrono behind the Ohler 35 to check to see how close the 2 read. Their was about a 1% difference and the Chrono gave higher reading than did the Ohler. IMHO the Ohler with it's 3 screens is the more accurate of the 2 and IMHO the CED Millenium is the best new chronograph on the market today at a reasonable price.

Thanks, Nick. Always happy to get the straight skinny from an expert.

The problem with being an old phardt is that "they" keep changing the things we used to know!

Yes! Darn Them! :D

I have, by the way, an old fashioned break-wire chronometer I designed 20-odd years ago that can be used to cross-check a skyscreen chronograph. It just takes some plastic plumbing pipe to set up a wire holding frame fore and aft of the skyscreens. You measure the space between the wires (tin foil strips work well) and it measures the transit time in microseconds. You then use a pocket calculator to turn that time and your spacing into feet per second. To increase resolution, you increase the space between the wires. I'd like to set up a program for cross-checking different chronograph brands, but I own only two and already know my Dad's isn't good. If you have access to try more brands through your business connections and want to borrow the thing, let me know? The only drawback is it predates common LCD displays, so it has a LED readout, which you sometimes have to shade to make it out in bright light.

JWP475 is spot on, as usual. My CED and Oehler are rather astonishingly within 5 fps or so of one another out of 2500 fps. I have moved the CED in front of and behind the Oehler and averaged the resulting differences to get that result. That is with the CED's IR light source option installed and operating on an inverter driven by a motorcycle battery. They have optional rechargeable batteries, but I already had the inverter rig for running my laptop for long periods of strain gauge testing.

Nick indirectly points out another factor with his last sentence - computers are sensitive to changes in voltage, and can do odd things when it isn't right. Having a consistent power source, or at least checking battery voltage before you leave the house, may well solve some chonograph problems.

For those of you who have the simple Shooting Chrony and wish you had the remote control model, you can make a simple push button remote that will let you toggle thru your reading without having to walk out to the Chrony. Here is a link to the schematic.

http://www.noplabs.com/chrony/remotecontrol.html

I've had one for years, but I just don't use it.

T