Home Forums Hunting & Shooting Ask The Gunwriters Chronograph function/Weirdness question

So wondering if anyone has seen this before.

I have an Oehler 35P. I have chrono'd loads for my 260 consistently at around 2725, give or take.

Friday, I took it out and tried to chrono the ELDX loads I am making for my 300. Got a lot of errors that I attributed to the lateness of the day and bad lighting.

So I came back today and reshot the loads and for kicks, shot some of my old 260 loads.

Well, oddly,no errors, but all the loads came back running quite a bit slower...like 60 to 80 fps slower. Even the same loads I shot on friday.

Temps were the same in all conditions, as I have it noted in my log. Cases, primer, powder, bullets, rifles, distance to chrono, everything...all the same.

I talked with Oehler, and will stop by probably tomorrow, they suggested just light conditions could cause this, differing times of year etc.

Not real happy if that turns out to be the case. I really want to know the velocity so I can figure come ups etc.

Anyone else experienced this?

On a good note, the new 300 looks to shoot the ELDX's pretty well, does not seem picky at all and, at least accuracy wise, will do the trick for me, at least the initial results appear to indicate that.

I have definitely seen similar results with my ProChrono in midwinter due to the low sun angle. That would be my guess. I seem to get somewhat better results doing my testing in late morning, and knocking off by one o'clock or so. If I try to continue testing the readings start getting noticeably less reliable before two o'clock and then it starts missing shots.

Some midwinter days the chrono basically refuses to work well at all. I almost always do my test shooting west to east which may either help or hurt, I don't know.

I had the same thing happen the other day. I was indoors so temp wasn't a factor, using a magnetospeed so light was not an issue. All same components. Only thing I can think of is the Lot of powder is different. Another possible variable would be the scale, its the same one but maybe it loaded a tad bit light??

would a supplemental light source help?

catorres1 - I have experienced exactly the same thing with my 35P, though it doesn't happen frequently. The 60- 80 fps variances in readings are probably not significant from a practical field (hunting) perspective. Nevertheless, we would like to have accurate figures and that's likely what we're getting based on ambient conditions at the time of chronographing.

I've found, as others have, that normal day-to-day variances of a few fps to 25 or 30 fps are common with most chronographs. Again, this can probably be attributed to conditions.

I bough my 35P new twenty-five years ago. The main unit was sent back to Oehler for a rebuild about ten years ago. It gets used a lot, year 'round in temperatures varying from 25 - 90 degrees, though virtually all shooting is done between 8 and 11 AM. Good luck with your efforts-

Guys -

I only have a O-33 so it's not the same unit. Also I never had or used the diffuser screens --that may have some effect ??

I bought mine in 1981 and it has been used A LOT. A couple of yrs ago I replace the light screens (photo screens).

To The Point --

In all my yrs of 'graphing I had VERY FEW miss reads/shot error, etc.


A long time ago I discovered - probably read the suggestion somewhere - that I got best results EITHER:

A- graphing in the shade on sunny days.

B- graphing on CLOUDY days.

Either way - Sun angle importance is diminished.

Just passing along 'something' that might help.


Jerry

Guys,

Thanks so much for the responses. Honestly, I don't know what to think, definitely not real happy to hear that this is sort of a 'feature'. Kinda hard to figure come ups and wind drift for long range shooting when you don't really know how fast your bullet is moving.

I thought I might get a Magnetoscope instead to avoid the whole light problem, but sounds like maybe that would not solve the problem either.

20 FPS is no big deal, obviously, but some strings were 100 fps low, but most averaged more like 60ish.

Anyway, I live in Austin, so I am going over to Oehler today or tomorrow for them to check the entire machine out. Really nice people, hopefully they find something wrong.

Otherwise, I am stuck with a lot of conflicting data and no way to tell which is right!

I've found the Oehler people to be quite helpful. Let us know what they say.

Many ways to skin a cat but my approach is to get an idea of velocity (with a chrono) and then confirm drops/dope to verify velocity. The chronograph certainly gets me in the game but confirmation is at the range.

As to the magnetospeed, I've put thousands of rounds over one and never a dropped shot. The velocities I've documented for different loads have been in excellent agreement with the dope verification. I fought ambient light issues with optical/light gate chronographs prior to the magnetospeed so I can feel the frustration.

Illumination does make a measurable difference with my Shooting Chrony. With the screens in place, I get one set of readings (which I think are the correct ones). But if the sun goes behind a cloud, the readings definitely drop if the screens still in place.

My rule of thumb is that I only chronograph between about 10:30 and 2:30, and on days that the tripod and chronograph cast a visible shadow. That seems to give me consistent results.

In my workshop, I'm building an unfinished project shelf, but it isn't done yet. But on that shelf, I have the parts to do an all-weather light source for my chronograph.

Denton - I really like the idea of an all-weather light source. Given my inability to control such things as wind, sun angle, and overcast, if I want to do any shooting at all, I have to do so when conditions are not always ideal.

For many of the posters, your problem could possibly stem from the fact that you have failed to include "ambient" when discussing conditions.

One suggestion they gave me over the phone was to 'blacken' the ogive of each bullet. He said it would protect from unwanted glints and be more consistent in the read.

Like I said, I really hope it just needs a tuneup or something, because this level of inconsistency is not what I hoped for.

I've taped sensor eyes, blackened bullets, and made a "shade" for the wind to catch and tip over the tripod. None of them seemed to level out the readings on a Shooting Chrony.

Okay, that's interesting. You're using a Shooting Chrony and I'm using an O-33, so that could have some influence on our results. I'm NOT an Oehler snob.

I don't remember 'comparing' speeds With Sun and W/O Sun. However overall I didn't notice any real difference in results. IF there was, it was small.

<<IF>> my results are slower in cloudy/shady setting that would be fine. I've been happy with the speeds recorded.


I have SEVERAL notebooks with Load Data/Graph Results/Targets for many rifles-cals-cartridges. I stated in my first post that I have graphed "A LOT" and that's not an exaggeration.

____________________________________________________________

Catorres1--If Oehler doesn't find something amiss and fix it..........DON'T give up on your 35, it is top of the line IMO.

TRY graphing in the SHADE of some sort. I'm really surprised that your are getting many 'error' readings.

Lots of Luck

Jerry

[quote=denton]
My rule of thumb is that I only chronograph between about 10:30 and 2:30, and on days that the tripod and chronograph cast a visible shadow. That seems to give me consistent results.
[/quote


We had a couple of those days up here in the NorthEast last summer.

How did your "proof" velocities compare to the primaries?

I believe there is a built in "alert" if they differ by a certain amount (depending on screen spacing).

See: http://www.oehler-research.com/custom/specs.html

For what it is worth, I never do chrono work without a tape measure and checking screen spacing. It is too easy for them to get bumped off a little. Doesn't take much. On .308 match loads, 1/8" on a 2' spacing made ~50 fps variance.

Whatever it is, you will not find better service than with Oehler Research.

Good people that make, and stand behind, good equipment.

Unfortunately, I do not have the one with the printer. If I had known how useful it was, I would have ordered one with it, but I did not.

What that means is that the numbers blink where there is a discrepency, but I can't see what the readings are. Bummer.

Anyway, I'll be at Oehler tomorrow, hopefully, they can help out. But if I go away with only an explanation of lower sun for the time of year or whatever, I don't know how useful I'll find this. That would mean I can only trust it if I use it the same month every year. Not very helpful, so hopefully I'll get a better resolution.

I did talk to a friend who may be able to pass me on a free magnetospeed or whatever it's called, that he has, as he got a couple via a demo or something like that....it's a log shot, but not an impossibility....

I've had very consistent results with my Oehler 35P in different light conditions, but do admit to not chronographing much when the sun's real low.

Also should point out that it's common for the average of two different strings of one load to vary somewhat, even in the same light conditions, or when using a Magnetospeed. A lot depends on how many rounds you shoot.

I think the printer can be added.

Sounds to me like a screen spacing error. I've had it happen to me before. Can be particularly easy to experience if you use short (2') spacing.

I have also used Oehler equipment in varying light conditions.

They will get to the bottom of it.

Low sun angles have definitely caused problems for me. Cloudy to cloudless days not so much. Partially worked out a design for a chronograph and the optics, which I'm not so good at, were definitely difficult. The sensor circuit a little less so since it has to compensate for a very wide range of light levels, and both screen sensors must make close to the same compensation.

(Denton - 4 ft screen spacing, widest angle stock LEDs I could find, overlapping half power points, good diffuser, sensor circuit optimized to match. And well shielded from ambient which made it all too cumbersome for my modest needs. PIC MCU, I love those things.)