I just got an Oehler 35P with the three screens. It comes with a 2 foot bar for the screens but suggests that the longer the bar, the more accurate the readings.

Conduit is cheap. I made an 8 foot bar, supported by two camera tripods. (Tripods and light stands are NOT cheap.) The bar is sort of a pain in the butt to set up and so I have it all assembled with the wiring secured in place. It fits in the truck, and I can store it in a stairwell . . .

But, with length comes the downside of getting the bullet to fly through the screen "window" and not hit the screen. It's long, cumbersome, awkward. That two foot bar is looking pretty damned convenient.

We're timing varmint rifles in the 4K fps realm.

How long is "long enough" ???

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I have an Oehler 43 and went with the 4 ft pipe as an option. It and 3 screens work perfectly. I use 2 Oehler supplied tripods. No complaints on any Oehler products, only praise. My setup has no problem with a .22-250 in the 3800's.

I use the 4 foot- not quite as "good" as 8 or 16, but easier to handle and store. I do many high vel 22's.

CED maintains that there is only little increase in accuracy when you extend spacing.
I am not so sure.
Setup is a snap when you attach a little ($5-)laser at the barrel and install the brackets "around" the laser beam.

The difference in the two foot and the four foot spacing (provided the screens are spaced EXACTLY two or four feet, respectively) is, for a bullet at approximately 3000 fps, a minimum precision level of 4 to 5 fps for the two foot spacing and about 2 fps for the 4 foot spacing.

The counter is based on a 1 million hertz chip. At approximately 3000 fps, if the two foot screen spacing counts 666 "beats", then the machine will register 3003 fps, while if it counts 667 "beats", you will get 2998 fps. By the same token, on a four foot spacing with a 1333 beat count, your registered velocity will be 3001 vs. a 1334 beat count at 2999.

Actually, error in properly measuring screen spacing has a larger effect. If you miss a two foot screen spacing by one-quarter inch, this is approximately 1%, or 30 fps at 3000 fps. Misspaced screens are less important with a wider screen spacing since the same quarter-inch error would only be .5% for a four foot spacing, or about 15 fps at 3000 fps.

By the same token, screen "windows" are pretty generous on todays screens. On the shorter screen spacings, it is possible to shoot across the screens at a significant angle. This would have the effect of lengthening the space between the screens and registering a lower velocity.

In other words, with a 1,000,000 hertz counter, worry more about the ACCURACY of your screen spacing than the spacing itself.

I have always used a 4' spacing with my Oehler 35, but that's only because I'm still using the same 5' piece of aluminum conduit that I bought for my original Oehler Model 10 some 33 years ago (the Model 10 was a 400,000 hertz model, for which Dr. Oehler recommended a 5' screen spacing, and boy, were those paper screens a bitch!) The good Dr. Oehler was located in Pflugerville, just outside of Austin in those days. I was a college student at the time and he was kind enough to receive me and my good friend in his home/workshop/factory and show us more than we ever thought we might know about chronographs. We scraped together $110 between us to buy one of his original models. He took pity on us and gave us a whole potload of slightly defective paper screens, which we "repaired" with judicious use of scissors and a bottle of silver circuit print. Now those WERE the good old days!

See!

That's why this forum is so good. Posted about 4 hrs ago and have several detailed answers already. What a deal!

Thanks

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.223 Ackley Improved Wildcat Forum:
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G - I also use the 4ft pipe. Get a handful of plastic zip ties and bundle your wire. I color coded each plug for the start/mid/stop feeds and the back of the printer/display unit. This really helps when setting up your chrono at the range.

One helpful hint - make sure you carefully measure the attachment points on your rail. A few centimeters off will be reflected in different readings between the standard screen and the proof screen. This is especially true if you are going to use the shorter mounting rods.

Another helpful hint - make sure your carry an extra 9 volt battery and printer paper. Unplug the start screen between long periods to conserve battery power. I can almost get through an entire shooting season on one battery. I use my Oehler almost every time I shoot at the range.

ZD~
Another shooter and owner of a 35P, and I, have a running argument over the subject of disconnecting the printer during lulls. Except for the LCD which draws a miniscule amount power, there is little or no drain on a battery when it's reading nothing. However, if you reattach the cable to turn it back on, there is significant drain when it activates the printer to cycle for the "ready". I say you draw more power hooking and unhooking it than leaving it be, which is what I do with mine. In four hour sessions twice a week mine stays hooked up and I don't use as many batteries as my friend in a year. I usually go through two or less in a shooting season. Do you have any information on the draw of each method? I still say it's preferred to not unplug.

General comment, I use the 2' conduit. The 10 fps, or less, of loss in accuracy with the shorter spacing has no practical effect for our use. It enables me to carry the entire setup neatly in a cheap Doskocil two rifle plastic case and facilitates storage. For the connectors I purchased 20' of plastic spiral wrap at an electronics supply house and encased the wires in that, starting the wrap at the screens. The short wire from the rear screen then plugs into the printer nearest the left edge of the printer as you face it, the median length goes to the middle plug and the longest one from the front screen, the on/off, plugs into the middle of the printer. The plastic spiral wrap keeps the wires from abrading, they're organized, and easy to loop and circle to insert in the carrying case.

Bob - Me tinks de only folks with enough knowledge on this subject is Oehler. Very good point on the start up drain. Let me know if you find the answer.

Well . . . "Oregon mist" is keeping me from heading out for a "shootathon" for a couple days. (I'm retired, no big deal.)

I set up and ran air rifle/pistol tests on the 4 foot bar. Everything is very precise. Four foot bar is MUCH easier to manage! I can live with some error. That 8 foot bar is a hazard and a nusiance! The 4 foot bar runs nicely off one tripod. I returned the second tripod for a refund. (The money is nice.)

I secured cables to the bar and bound them together with wire ties -- neon yellow ones! I found some insulated/padded nylon "lunch bags" at Fry's Electronics for $3.00 and these are perfect for carrying the printer, and stowing the cables at the end of the bar.

Three batteries and two rolls of printer tape. I'm anal retentive.

With the three screen setup you get two readings. The pellet guns are light weight enough that the bullet slows about 1 fps through the screens. I wondered if that was a measurement error on the bar spacing.

Double checked . . . Spacing is perfect. So, we turned the screens around backward and reconnected. I get the same readings either direction. This seems a useful check.

What about light rain? I'm asking Oehler, but this forum is faster with answers. I can keep the printer unit out of the rain, but what about the screens? Not a deluge, just that "Oregon mist" stuff. You know . . . not enough to get out of, but still not dry weather.

[This message has been edited by Genghis (edited 04-27-2002).]

Another 35P owner here.....with 4 foot spacing. I love having the printer. For the extra $50 it's worth getting the two stands and four foot rail. It all packs into a plastic shotgun case. Every shooter needs one of these.

Don`t know about "Oregon Mist" but I`ve played around in "Canadian Mist" after a range session a time or two

I found my Pact doesn`t work well in the rain. The water collects on the sensors and screws with their picking up the bullet.

I'm using a 4 foot rail. It all packs into a bow hunting case -- sorta clunky, but even the tripod fits inside.

Yesterday I ran the stuff in rain/hail. I put a hat over the printer. The sceens mostly screened out rain/hail. That's the "liquid sunshine" we get around here.

Unit is most excellent.

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