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Posted: 7/7/2009 7:13:09 AM EDT
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I have a Chrony Gamma Master chronograph that I've never gotten a chance to really set up and wring out. I'd like to not waste a lot of ammunition playing around with it, but I still think I need plenty of practice before I start "knowing what I'm doing." The Chrony manual is...less than clear in a number of areas, which doesn't help.
Can someone post a straightforward, step-by-step explanation of what to do, how to do it, and how to know you've done it right? |
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Here are some of my general ideas on using your chronograph of whatever brand:
Placement Chronographs need to be placed a uniform distance from the muzzle of the gun. Your data will vary a bit with distance. I would pick out a standard distance and use that distance every time. You need to have the screens far enough from the muzzle to keep muzzle blast from messing up the readings. It seems as if 10, 12, and 15 feet from the muzzle seem to be the most popular distances. Normally a camera tripod is used. Make sure things are steady. When in use, watch how the muzzle blast affects the chronograph screens. Make sure that you have compensated for the lower muzzle and actual bullet path as compared to what you might see (and therefore think) as the bullet path, which is actually the sight path as viewed through the scope or iron sights (which is higher). Shooting the chronograph or screens is not a good start! Line up the sights (keeping in mind the actual bullet path) with the screens and the target beyond. Raise, lower, level and move side-to-side the chronograph tripod as needed. A second person really saves time here, if possible. Skyscreens issues Skyscreens or rods need to be full extended. Make sure the rods on a Chrony are all the way up or you will get errors. Light conditions must be proper. Chronographing with the sun low in the sky can cause errors. In fact cloudy or overcast days are preferable to blue sunshine days because the light is more diffused. If you are having problems, use something to diffuse the light above the sky screens. If not supplied with the chronograph you sometimes can jury-rig something like a piece of plastic lighting panel like those used in overhead fluorescent lights. I would plan for this in advance because range fixes are rare. How many shots? Many of us feel that maybe we can get by with 3 shots. Well, 3 shots will tell you something but is not statistically accurate. 5 shots should be the minimum, 10 shots are, of course, much better, but experts in chronographing tell us that 7 shots is actually a very good number for accurate statistics. In a revolver I would at least go all the way around the cylinder for a minimum of 6 rounds. 12 would be better. Velocity goals and background research You may be looking for safe minimum pressure for your light loads or practical maximum velocity for your hunting or defense loads, or something in-between. If you are chronographing as a matter of working up a handload, you need to know what the expected velocity of maximum load is with the powder you are using. You can get this info by comparing loads with the same powder and bullet weight from different reloading manuals and sources. In fact, keep in mind the general maximum velocity area for that cartridge/bullet weight. For example: most sources will have a maximum velocity for the .223 Remington and a 55-gr bullet around 3100-3200 fps. Keep this figure in mind and DO NOT EXCEED. Also do not exceed the velocity given for the particular powder you are using - which may be less than norm for the cartridge/bullet weight because it is faster burning and reaches maximum pressure sooner than "standard" velocity is reached. An even more accurate method of duplicating safe factory velocity/pressure is to actually fire factory ammo of the same bullet weight from your gun. The average velocity given will be an excellent guide as to how far you can go safely. Remember that 5.56mm military ammo (M193 & M855) is loaded to higher pressure and velocity than SAAMI .223. In my 20" AR M193 will go 3240 fps. I do not want to load my handloads (non-crimped primers in fired brass) that hot - so stay at least 50 or more fps under figures generated by 5.56 military ammo. How can the chronograph aid us in establishing safe loads - Or finding the practical maximum (or working) velocity? So with a chronograph I am able to compare my loads with factory (read: safe-pressure) loads that have been shot from my particular rifle or handgun and work up to that velocity if I desire. Or at least compare them to what an average of reloading handbooks are getting from that load as far as velocity. So it works as an AID OR ADJUTANT TO OTHER ESTABLISHED PRESSURE SIGNS and can often be your FIRST warning sign. It can also answer some questions on what a load is doing that seems somewhat odd when compared to what was expected in the reloading manual. John Barsness [via Internet] reports that in his testing experience: “I worked up loads in 3 different cartridges (.22 Hornet, .270 Winchester and .30-06) using all the old-fashioned methods: bolt lift, primer appearance, measuring the case head, etc. Then I had the same "maximum" loads tested at the Western Powders lab. If I remember correctly, in the .22 Hornet the pressures of my handloads were about right, in the .270 they were too high (around 68,000 psi), and in the .30-06 a little low. Using a chronograph was a more accurate predictor of pressure than the old-fashioned methods. Why is this so? What do the experts say? "Muzzle velocity for a selected load is a function of the mean effective pressure and the barrel length." - Lloyd E. Brownell, Ph.D. - Firearms Pressure Factors, Wolfe Publishing Co. "Because velocity is the by-product of pressure, a chronograph can, albeit indirectly, give you an insight into pressure being developed by a given load. While a chronograph is no substitute for a pressure gun, your velocity data can alert you to potentially dangerous pressures before you're stuck trying to super glue your receiver back together." - Barnes Bullets #2, Ronin Colman, "What Do You Do With A Chronograph?" "The best predictor of pressure is a chronograph. If you're getting muzzle velocities noticeably higher than is common for that cartridge, powder and bullet, then your pressures are higher than they should be. It's that simple. If you work up loads using that rule, then you don't need to look at fired cases, because the pressure will never get high enough to form ejector-hole marks on the case heads or blow primers. ...next to real pressure equipment, a chronograph is the best guide to excessive pressure for the home handloader. There are no “magic barrels” that allow another 100 to 200 fps"! - Handloader, June 2004, “More Pressure Experiments”, John Barsness. "A chronograph does many things for the handloader. Obviously it indicates just how fast the bullet is going, but it also tells us how consistently the bullet leaves the muzzle. This may or may not have any bearing on accuracy, at least at "normal" ranges, and holes in the target are the ultimate measure of consistency. But when things are perking right, the chronograph is one more indicator of consistency. More importantly - Think of the firearm as a single-stroke internal combustion engine with an expendable piston, the bullet. Everything else being equal, a certain average pressure will always produce the same velocity. This means that, everything else being equal, if the velocity changes so did the pressure..." - Handloader editor Dave Scovill. "One of the most valuable applications for a chronograph is in keeping loads safer. Loading manuals provide a guide, generally suggesting a starting and maximum load. These load recipes are determined by careful loading and pressure testing. Maximum loads are based upon industry standard chamber pressure criteria. Generally speaking, with a given set of components, the higher the velocity, the higher the chamber pressure that is required to produce the velocity. If one of your loads produces velocity in excess of what a loading manual indicates, you can also assume that the pressure is in excess. If the velocity of one of your loads equals the maximum listed velocity in the loading manual (with a comparable barrel length), it’s prudent not to exceed the powder charge level you’re using, even though the quantity of powder you’re using might be less than what is suggested as the maximum quantity in the manual." - Accurate Arms Loading Guide #1 - Chronographing Metallic Ammunition - Rick Jamison. Make a "Benchmark" or "95% Solution" Reference Load Credit gunwriter Rocky Raab for this method that allows users of a chronograph the luxury of changing load components and finding a safe new "pet" load with a minimum of shots fired and maximum reference to what has been safe before. It was featured in the Jul-Sept 2009 issue of "The Varmint Hunter" magazine and is found in its entirety on Raab's website here: The 95% Solution "One of the most common questions I get goes something like, “If I change to magnum primers, or a different make of bullet, or a different lot number of powder, do I really have to go back to Start loads and work back up?” The answer is “Yes” — but also “No.” Changing components has been absolutely proven beyond any doubt to change the way loads shoot. The change might be in velocity or accuracy, but more importantly, also in pressure. So backing down a bit -especially if your previous load was on the warm side - is vital. The key words there are “a bit.” Backing all the way down to Start loads is safest, but working slowly back up might waste an awful lot of expensive components, not to mention the time it takes or the wear and tear on the gun. So how far do we really have to back off in order to re-test? Without a known test point, we cannot tell. Have a fully documented load that is ALWAYS safe, even if you switch components. When you do switch components, you can match the performance of a load using that switched component with the known load, and know right away if the new component delivers less, the same or more velocity/pressure. That known (benchmark) load is The 95% Solution. Here’s how you find it. Once you have a preferred or “pet” load worked up with a given list of components, write down EXACTLY what all those components are. List not only the maker but even the lot number of every component (if you know the lot numbers). List the brass, the primer, the powder and the bullet. Also record exactly how that load performs in a given gun. As a minimum, list the average velocity, extreme spread and standard deviation. If you can measure the pressure, record that average, ES and SD as well. The least important number (for this use) is the accuracy, so that’s optional. Do this for every single cartridge you reload. Much of it is probably in your load notes already, except for lot numbers. You now have complete data for your pet load. To establish your 95%S, you simply take your pet load, with the exact components you listed, and decrease the powder charge to 95% of the pet load’s charge. Yup, that’s why it’s called The 95% Solution. Note that we are NOT talking about a load that’s at 95% of the book maximum charge. We want a load with 95% of the powder in your favorite or “pet” load. Read that again. It’s vital. Now load and fire at least ten of the 95%S load. Carefully record every performance number we talked about before for velocity and for pressure if possible. Again, accuracy is unimportant because the 95%S isn’t a load we’ll be using in the field. The more 95%S rounds you test here, the more reliable will be the performance numbers, but ten is a minimum. When the time comes that you have to buy a new box of bullets or another can of powder, or switch any other loading component, the first thing you do is to load up ten rounds using the 95%S recipe – but with only the one new component changed. (It’s pointless to do this if you change two components, because you have no way to tell which of them causes any change in performance.) With that single substitution, test and record the performance numbers. You can get only one of three possible results: the performance will be the same as the 95%S, less than the 95%S, or it will be higher. If the performance of the test load is the same as the 95%S load, you can simply go back to your pet load and KNOW that the new component changes nothing. This is the ideal situation, and you were able to determine it with only ten test shots. Isn’t that great?" |
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See the first response. Get a printer, they have controls that are more intuitive.
The Chrony manual blows. It's so poorly written I gave up on trying to re-write it into an easy to use format. The other thing to do is shoot a BB gun across the chronograph to learn how to use it before taking it to the range. Or use a .22 RF at the range to save money. Get some 1/8th inch dowels to place in the holes for the sky screens. Add a piece of tape 4 inches above the instrument body on each stick - that defines the bullet path across the instrument. Get in front of the chronograph and look directly down the gun bore to get it aligned. Take the bolt out if possible. (  )
Sometimes only a little misalignment is required to cause bad readings. A common example is shooting on a target at 100 yards, then switching to a target on the frame for the next lane, but down at 200 yards. Same thing for shooting from one side of a wide target frame to the other; the chronograph needs to be realigned. That is enough misaligment to cause a failure. Watch the folding body on a Chrony. Make sure it is completely open. Just a few degrees closed is too little to notice from the bench, yet can shorten the path to cause the measured speed to increase 200 fps. The Chrony needs to be level for the same reason. |
| As stated do not use the metal rods that come with the "Crony" brand units, use dowels (the round wooden chopsticks from take-out places work good). Why you ask? Even if you do not shoot the crony, if you hit the rod (seen it happen twice) the impact will break the plastic crony body where the metal rod goes in, the wood breaks with out the stress on the plastic. I have the Beta Master with the remote screen and it is pretty easy to use. Do not set up a target to shoot at just blank backstop. You want to concentrate on shooting OVER the CENTER of the crony. I use a tall tripod so I can shoot standing up. The hardest thing I have found is clearing the memory of the unit, I allways have to read the directions to do it. |
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Pete, Aero and ElJay, thanks for the extremely useful information. I'd taken the thing to the range once, and whether it was because of lighting or alignment or whatever else, I couldn't get anything like a consistent reading on what I though was decent .22s. I'm going to buy a cheap BB gun to practice with the chrony so I get things to work. Aero, the package I got came with the printer, so that's a big plus. It looks like the printer will control the unit, so I'll dig into using that and see what I come up with.
I hadn't thought about those steel rods being a potential problem. I'll buy some wooden dowels of the appropriate size and use them "just in case." If anyone else has great stuff like this, PLEASE post it! I've learned a lot more from 5 minutes of reading this thread than from several hours horsing around with my chrony. Now I just need to find a cheap BB gun... |
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Huh. I have had a Master Gamma for years. I bought it in 2001, used it once, lent it to a friend. After much nagging, he finally collected all the pieces and gave it back to me in 2005 or so. Except the instruction manual, which he had lost. All I had was the summary page of commands from the back of the manual, which I had photocopied and laminated to use as a quick reference quide.
With that one page, I have had absolutely no problems learning, relearning and using my Chrony. The machine works exactly as described. The tips on setting up for consistent readings that are listed here, are in the manual. The tip about the wooden dowels that is mentioned here is in the manual. There is nothing wrong with the manual. You only use about three functions on the silly thing anyway. Change strings, review results, erase. And yes, the printer works as a control unit, but it only has one extra button, so it doesn't make things significantly simpler. In fact I found the buttons on mine to be a bit sticky, whereas the ones on the unit are nice and positive, so I stick with them. |
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