Chronographs

[gcamp54]

Oehler's web site:

Model 35P System, complete

Thanks.

Gordon

 

[Pdvdh]

Phorwath,

I have no argument at all.

I don't believe absolute knowledge of the actual velocity is necessary or even possible considering variables in BC, rifle,conditions,etc. Consistency is much more critical than absolute accuracy in a chronograph.

I am in pursuit of knowing my MV as accurately as possible. as I believe it to be completely necessary for any ballistics program to dope my down-range hits under the variable conditions I hunt in. These conditions include elevations from sea level to 7000' ASL, temperatures from 32F to 75F, and sloping shots up to 35 degrees. I have no way to field confirm, and then develop drop charts for these variable conditions. I've proven the accuracy of my ballistics program in the locations I am able to field test it against measured down-range drops. Now I want to know the actual MV of my bullet, to give the ballistic software a chance of predicting the proper dope under the variable conditions that I later engage game under. So I think the importance of knowing the MV - as closely as possible - is all relative to the end users' needs.

That's the value of the in-field ballistics program, in my opinion. If I always hunted in the same location, and only shot at animals in a few locations, I could simply develop a drop chart for that location(s). Then I might not need to know my MV at all. Simply rely on the drop chart.

And reliably confirming the ES and SD is important to any LRH, unless he's willing to live with vertical stringing at extreme ranges.

I also confirm the BC of my bullet by recording down-range velocity at 1000 yds. Now with both MV and bullet BC confirmed out of my rifle, a good ballistics program will be able to provide me with the proper dope for my shots under widely varying conditions. Conditions that I'm unable to confirm field drops for prior to, or during, the hunt - prior to taking the shot. Unless, perhaps, I'm in a situation with circumstances that allow me to take a sighter shot off to the side of the game animal on the hillside where I can see the bullet impact, prior to then shooting at the animal.

One thing that I haven't mentioned, is the waste of my time that's prevented with the multiple chronographs. I will typically dismiss any load that yields an ES greater than 35-40 fps instantly during load development. For example, if my first two shots vary in MV by more than 40 fps, I won't even spend any more time on that specific load - if the multiple velocity data confirm my chronograph data are valid.

In the past when I only used one chronograph, I'm certain that I've wasted time on load development by respecting bogus chronograph data. Without any way of knowing better, I would respect the data. Possibly discarding a good load, or sticking with a bad load longer than necessary.

 

[Pdvdh]

Now I gotta give Paul some credit for making at least one guy put on his thinking cap! Two revisions I'd like to see Pact do; first is to lengthen the distance between the screens to 36" or one meter. Locate them with dowl pins. I just have an idea in the back of my head that a 36" spacing might be better. Secondly, I think Pact needs to make a major change in their system. Make a provision for a third screen in case you want one. Then all of them need to add a device to insert an SD card in there to save all your shooting data. With that you can simply down load the data into your PC for future reference. I also prefer the older light bar better than their new bracket.
gary

If a chronograph will provide two velocities for each shot fired, it doesn't matter if it's the highest quality unit in the world or not. Because the more important trait is being able to identify the shots that result in the recording of bogus velocity data. And my experience matches Oehler's own statements, as printed in their 35P Owner's Manual. All chronographs will occasionally fart out bad data.

I like my skyscreens separated by as great a distance as is reasonably possible to still result in a packable unit. As you know, the closer the screens are mounted together, the greater the error in the recorded velocities associated with any minor spacing error between the screens. I've settled on 5-6 feet of separation. What I like about the Oehler units I have, and the vintage PACT PC2, is that they provide the option of programming their chronograph units to varying skyscreen separation distances. I can program 2 feet or 20 feet of skyscreen separation into the Oehler units, if I desire.

I really do like the print feature on the Oehler 35P. Each shot velocity is printed out on paper. No losing that data once it's been printed out on the paper. Doesn't matter if the battery goes dead, or the unit is stuck by lightning or a bullet from a terrorist.

All in all, I could be content with my old and well used, vintage PACT PC2, and Oehler 33. Provided that they're run in tandem and produce two velocities for each bullet fired. Having the 35P added into the mix and receiving four velocities for each shot fired is even nicer - of course. It provides almost overkill assurance that I'm able to ID good data from bad data. And I'm happy that I'm running the three units concurrently. I would do it again. That's just me. But I could never be content relying on a single chronograph that provides only one record of velocity for each bullet fired. Not after experiencing life with two recorded velocities for each shot fired.

It would be wonderful if PACT would move in the direction of a proof channel on one of their units. Don't know how much the cost would have to be increased, but that's the best single feature any chronograph manufacturer could include for the serious chronograph user, in my opinion.

 

[Trickymissfit]

Oehler's web site:

Model 35P System, complete

glad to see Ohler start putting the unit in a case. Doug's just came in a card board box, and he couldn't find anything at the time that was tall enough for it. A trip to Menards for some lumber and an afternoon with the miter box fixed that!
gary

 

[Trickymissfit]

If a chronograph will provide two velocities for each shot fired, it doesn't matter if it's the highest quality unit in the world or not. Because the more important trait is being able to identify the shots that result in the recording of bogus velocity data. And my experience matches Oehler's own statements, as printed in their 35P Owner's Manual. All chronographs will occasionally fart out bad data.

I like my skyscreens separated by as great a distance as is reasonably possible to still result in a packable unit. As you know, the closer the screens are mounted together, the greater the error in the recorded velocities associated with any minor spacing error between the screens. I've settled on 5-6 feet of separation. What I like about the Oehler units I have, and the vintage PACT PC2, is that they provide the option of programming their chronograph units to varying skyscreen separation distances. I can program 2 feet or 20 feet of skyscreen separation into the Oehler units, if I desire.

I really do like the print feature on the Oehler 35P. Each shot velocity is printed out on paper. No losing that data once it's been printed out on the paper. Doesn't matter if the battery goes dead, or the unit is stuck by lightning or a bullet from a terrorist.

All in all, I could be content with my old and well used, vintage PACT PC2, and Oehler 33. Provided that they're run in tandem and produce two velocities for each bullet fired. Having the 35P added into the mix and receiving four velocities for each shot fired is even nicer - of course. It provides almost overkill assurance that I'm able to ID good data, from bad data. And I'm happy that I'm running the three units concurrently. I would do it again. That's just me. But I could never be content relying on a single chronograph that provides only one record of velocity for each bullet fired. Not after experiencing life with two recorded velocities for each shot fired.

It would be wonderful if PACT would move in the direction of a proof channel on one of their units. Don't know how much the cost would have to be increased, but that's the best single feature any chronograph manufacturer could include for the serious chronograph user, in my opinion.

I do not know what the cost of new screens would be this morning, but I had to buy a set a few years back thanks to my big feet. They were $27 a pair complete with cables. I doubt they are fifty dollars right now. The input could be done for about twenty dollars and the rest is software. I honestly believe that Pact could market a triple unit for under three hundred dollars. Out of the box I prefer the Pact light bar over anything on any chronograph I've ever seen, but it needs to be longer. Wouldn't hurt for them to do a three and four foot light bar as well. On the otherhand the cells we have today seem to react so much faster and consistently than even what we had ten years ago, so you must take that into thought. To take this further I think that Pact could market a unit with a printer driver, two USB ports, and an SD card reader with the triple cells for under $300. I prefer just the printer driver as to a built in unit due to the failure of printers so often. The USB ports could connect directly into a notebook PC with additional software to help you along in your journey to perfection. Lets hope they are listening!
gary

 

[Pdvdh]

On the other hand the cells we have today seem to react so much faster and consistently than even what we had ten years ago, so you must take that into thought.

Lets hope they are listening!
gary

Gary,
I'm not sure if I was clear as to why my preference for using the wider skyscreen spacings, in spite of faster processor times in the current day chronographs. I can mount my skyscreens pretty close to the exact separation distance programmed into the chronograph unit. But I can't know at what position over the skyscreens the bullet triggers the clock to start and stop. Some of the current model chronographs position the skyscreens as close as 18", without any ability to program the chronograph to process signals from greater skyscreen separation distances. At least one manufacturer told me that the larger skyscreen separation distances weren't necessary with their new lightning fast processors. But that doesn't satisfy my concern that a relatively small error in separation distance between the mounted skyscreens could still result in objectionable error. The slots through the top of my sky screens are about 1/8" wide. How can I know where over those slots the bullet triggers the chronograph clock to start and stop? Or that they both trigger at the same location over those slots?

Error with 18" skyscreen separation:
If I mount my skyscreens 18" apart but there's an error of 1/8" either less than, or greater than, the 18" which actually triggers the clock start and stop signals, then that 1/8" error will contribute to an error of (0.125"/18") * 100 = 0.69% in the calculated velocities. This error will exist for each shot fired, no matter how fast the state-of-the-art electronics in the modern chronograph processes the signals. With a true muzzle velocity of 3000 fps, the recorded velocity would be in error by 20.8 fps. A 20.8 fps error in muzzle velocity results in a 4.1" vertical doping error at 1000 yds with my 300 Win Mag, at standard atmospheric conditions, with a G7 bullet BC of 0.286, with a zero range of 315 yards. [Doping error determined with LoadBase 3.0 Ballistic Software Program.]

Error with 6' of skyscreen separation:
On the other hand, if I separate my skyscreens by 6 feet, and end up with a 1/8" error from the exact 6 foot separation distance between the start and stop signals, then the calculated error in bullet velocity will only be (0.125"/72") * 100 = 0.17%. With a true muzzle velocity of 3000 fps, the recorded velocity would be in error by 5.2 fps. This lesser error reduces my vertical doping error to a 1" error at 1000 yds with my 300 Win Mag, at standard atmospheric conditions, with a G7 bullet BC of 0.286, with a zero range of 315 yards. [Doping error determined with LoadBase 3.0 Ballistic Software Program.]

I believe I can mount the skyscreens on my one-piece skyscreen rail to within 1/8" of the exact target measurement quite easily - say 18" - with a little bit of patience, care, and attention. But I can't be certain that the bullet actually triggers the start and stop clock over that 18" of separation? So that's primarily why I run with 6 feet of sky screen separation, in spite of the speed of the processors in any of my chronograph units. If there is an 1/8" or 3/16" error beyond my control, I want to minimize the error in the velocity calculated by the chronograph.

I prefer the 1" of vertical POI error at 1000 yds, compared to the potential 4.1" vertical error with the 18" skyscreen spacing.

 

[Trickymissfit]

Gary,
I'm not sure if I was clear as to why my preference for using the wider skyscreen spacings, in spite of faster processor times in the current day chronographs. I can mount my skyscreens pretty close to the exact separation distance programmed into the chronograph unit. But I can't know at what position over the skyscreens the bullet triggers the clock to start and stop. Some of the current model chronographs position the skyscreens as close as 18", without any ability to program the chronograph to process signals from greater skyscreen separation distances. At least one manufacturer told me that the larger skyscreen separation distances weren't necessary with their new lightning fast processors. But that doesn't satisfy my concern that a relatively small error in separation distance between the mounted skyscreens could still result in objectionable error. The slots through the top of my sky screens are about 1/8" wide. How can I know where over those slots the bullet triggers the chronograph clock to start and stop? Or that they both trigger at the same location over those slots?

Error with 18" skyscreen separation:
If I mount my skyscreens 18" apart but there's an error of 1/8" either less than, or greater than, the 18" which actually triggers the clock start and stop signals, then that 1/8" error will contribute to an error of (0.125"/18") * 100 = 0.69% in the calculated velocities. This error will exist for each shot fired, no matter how fast the state-of-the-art electronics in the modern chronograph processes the signals. With a true muzzle velocity of 3000 fps, the recorded velocity would be in error by 20.8 fps. A 20.8 fps error in muzzle velocity results in a 4.1" vertical doping error at 1000 yds with my 300 Win Mag, at standard atmospheric conditions, with a G7 bullet BC of 0.286, with a zero range of 315 yards. [Doping error determined with LoadBase 3.0 Ballistic Software Program.]

Error with 6' of skyscreen separation:
On the other hand, if I separate my skyscreens by 6 feet, and end up with a 1/8" error from the exact 6 foot separation distance between the start and stop signals, then the calculated error in bullet velocity will only be (0.125"/72") * 100 = 0.17%. With a true muzzle velocity of 3000 fps, the recorded velocity would be in error by 5.2 fps. This lesser error reduces my vertical doping error to a 1" error at 1000 yds with my 300 Win Mag, at standard atmospheric conditions, with a G7 bullet BC of 0.286, with a zero range of 315 yards. [Doping error determined with LoadBase 3.0 Ballistic Software Program.]

I believe I can mount the skyscreens on my one-piece skyscreen rail to within 1/8" of the exact target measurement quite easily - say 18" - with a little bit of patience, care, and attention. But I can't be certain that the bullet actually triggers the start and stop clock over that 18" of separation? So that's primarily why I run with 6 feet of sky screen separation, in spite of the speed of the processors in any of my chronograph units. If there is an 1/8" or 3/16" error beyond my control, I want to minimize the error in the velocity calculated by the chronograph.

I prefer the 1" of vertical POI error at 1000 yds, compared to the potential 4.1" vertical error with the 18" skyscreen spacing.

we are thinking the same. I think the idea of using an 18" screen spacing is not good, but to give it credit it does make for an easier setup. I'd much rather have a good solid 36" spacing, or even a 48" one. To be exact I may just build a 48" one if I can find the materials.
gary