Brent,
I'm glad to see there is brand loyalty out there and also happy to see that your Ohler chrony works as well as it does. For me to say I have "no experience" with Ohler, is to say I have not OWNED one. I've used them and yes, my ES was significantly better when using the Ohler machine. I just didn't beleive it. I have several friends at the range who own Ohler machines. When we go to the range, 2 of them, (both hall of famers) don't even get theirs out because they don't beleive it's worth the trouble and don't trust the numbers anyhow. Another friend, and former World's record holder says my Pact Professional is the nicest chronograph he's ever used. Personally, I like it but I'm not going to say it's better or worse than your Ohler, it just happens to be what I have. As for the extreme spreads being influenced by the chrony, I'd say they are more influenced by the shooter.
Lighter bullets are way more prone to velocity variation than heavy bullets. You are not going to get a 22-250 to shoot the kind of velocity spreads that a 300 Win mag will do. Given equal amounts of time and effort on each gun that is.
I shot perhaps 250 rounds at the range last year during test sessions, virtually all over my chronograph. A few I didn't care about. With no exception, the shots that my chronograph said were slow, came in low and the fast shots, came in high. I have all the targets, all were marked and spotted. All shots numbered. Never was there a group that didn't have complete coincidence with the chrony slip. If the chrony said 45fps, the group was 12" high. That's about the 7" my gun will shoot, plus the 5 extra for velocity. If the chrony said 110, it was 17-19 inches high. Low and behold, it knew which shots were high and low.
Our friend here is shooting a 22-250 at almost exactly the speed I shoot my swift. Mine is at 3705 average. At 450 yds (my close target distance out my living room window) My gun will consistantly shoot 55gr Balistic tips inside 3 inches. (10 shot groups). Sometimes It'll do down as far as 2. The velocity spread of 100fps at that range is going to add 1.3" of verticle. Now as the range increases, say to 700 yards, that same 100fps is now a 5.7" verticle. That's added to the group the gun will shoot. Now, I don't dispute the numbers you get from your machine, and I again, will be tickled pink if your happy. I would say that if you shoot your gun at longer range than you currently do, you will experience greater verticle patterning than you expect from the numbers you are receiving on your little slip of paper.
Next, as I said it may be the shooter. have you ever done any testing to see how the way you hold your gun affects bullet velocity? I'd guess no. So, here's the next excercise for you to try... Since your Ohler gives you great numbers, you should be able to see that when you hold your gun tightly against your shoulder, a 210Gr 30 cal bullet for example, will exit the muzzle aproximately 50-60fps faster than the same load allowing the gun to free recoil. Now as you become more familiar with the amounts of pressure that affect speed, you will see that "most" of the change happens with relatively light pressure on the buttstock. The holding tight only produces about the last 20% of variation. So, now we must assume that the shooter who regularly holds the gun at a comfortable pressure, generates as much velocity variation as does the ammo he/she has loaded.
On to chronographs. For approx 20years I have designed and built all sorts of non-contact measuring systems. Also, machine control systems, Written DNC systems, Built Optical Sensors, Hall Effect Devices, Microcontroller Industrial PLC's FROM SCRATCH, Etc, Etc, Etc. I've seen a few Phototransistors, Visible light sensors, and IR Sensors in my day. I even built 2 more a few weeks ago to go on our wire cloth loop. Ask Boyd, He's been to the shop to see them. Now, what you do to build a chronograph is you take a relatively fast microcontroller or a Digital Signal Processor (Faster Math Processor) and you let it count pulses from an oscillator. It gets triggered from a couple of Visible Light sensors to turn on and off. These sensors are connected with a uP Sample and hold circuit and then biased with a uP Digital Pot. Lets say for example that the sky produces a signal of 2.50000 volts. What we do is do a sample and hold on the value comming from the screen. Now Use an Op-amp and Digital Pot to offset that value to say 2.50010 volts. Send both values to a very high speed comparator and that result goes to the microprocessor that does the counting. This signal in not real smooth. Looking on an oscilloscope, you will find rather a lot of ripple, even in zero light. Now, the trouble is that the signal is only in PICO-AMPS. **** little current. (that's a digit behind a whole shitpile of zeros and a decimal!) Let's also say the wind blows and the picture our sensor sees is now of a little more cloud than before. Bingo, you have a trigger. The fact that the signal is so slight is what gives the chrony the ability to see a bullet traveling by. That same tight biasing of signals is what brings about false triggers. The fact of the matter is, they are so sensitive, (by nature) that they are signaling virtually all the time. The chronograph just picks out it's best guess of bullets or leaves/wind/...
Often times people shoot too close to thier screens and the shock motion of the bullet going by causes the second screen to trigger and might just give you a 5000 or 8000 fps reading as noted above. having a tree ANYWHERE near your chronograph will render the numbers useless. The lenses in your skyscreens (if you have disassembled them to look) give a very large field of view, larger than you think and will "SEE" leaves, branches, movement of any kind from as much as 30-40 Degrees LOS. Wind that shakes your tripod will make it see all sorts of things. There is even enough change in luminescence in differing areas of the sky to trigger the chrony.
You may or may not do any photography but if your familiar with a circular polarizer you will be intimately knowledgeable of the variation of angle and intensity of sunlight depending on your point of view. Point your index finger at the sun and rotate your hand and you will be locating all the places where you will get really cool pictures and sky backgrounds with your filter. The same applys for using a chronograph. Most that i've seen use a tubular style lens which is very directional. Not all are configured the same. Some may like being pointed at the sun, others may like being 90degrees from it. It will vary by brand. This could be why your chrony works differently than the other 2 you had. perhaps if you shot a different direction, you would hate Ohler and love some other brand. Had I been You, I would have at least tried to learn a little about why the machines work so as to be more effective when using them.
My greatest amount of experience with 2 chronys has been using my next door neighbors Shooting Chrony and My Pact. We use His at close range and shoot over mine at 450. We compared them and know that the numbers from his machine are 60fps faster than mine. I don't need to know any more. I can evaluate all the things I see and determine for myself if I think the chrony is wrong. Even when I thought it was, I was misled and wasn't looking at all the data in front of me. Once I learned more, I saw the machine was right. You do need to calibrate the balistics program to your chrony, and gun, and load, etc. A gun that doesn't stabilize a bullet perfectly will give an effectively lower BC than the theoritical number on the box and thus, will make you think your chronograph is wrong. It most likely is not. Just like a quarterback who throws a tight spiral like Kerry Collins will get a lot more speed and distance, with less drop on the ball than say a lame duck thrower like Dante Culpepper. Guns are the same. A .003 over throat allows the bullet to get a side cut off because it starts crooked and becomes a lame duck pass. It sheds velocity faster than a nice tight neck/throat and "good start" bullet as Hubie says. That will do all sorts of things that show up as velocity spread on a chronograph. Now, I'm sure you havent tested that yet so I'll tell you that I took a gun and rethroated it wrong just to see what it did. I even special ordered the throat reamer just to try it. Yep, it changed the ES, it changed the average velocity and it all showed up on my lowly old Pact.
As for thier code, the code on the web is the same thing you use, just without the equipment and yes, I think it's a peice of ****. Thanks to you, I now know the chronographs work much better than that.
