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New Oehler 35P, New skyscreen rail, First Test Data

 
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  #15  
Old 10-17-2010, 07:19 PM
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Re: New Oehler 35P, New skyscreen rail, First Test Data

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Originally Posted by phorwath View Post
Gary,
The extra cables in the photograph are the cables from the 7 different skyscreens I have mounted on my skyscreen rail. I wasn't shooting at the time of the photos. I simply draped the cables over the skyscreen rail while I was taking photographs to post in this Thread. There should be a total of 7 skyscreen cables. Three for the Oehler 35P, two for the Oehler 33, and two for the PACT.

Absolutely not!. All three units run and record velocity for each and every bullet fired - concurrently. This is the real value in running chronographs in tandem or triplicate. Two, three, or in my case, four sets of recorded data are collected for each bullet fired. This provides the additional data required in order to validate the quality of the data. There wouldn't be any good reason to shoot over mutliple chronographs if only one of them was used at any one time. I wouldn't bother purchase and setting up multiple units is I could only fire over them one at a time. Getting multiple velocities for each bullet fired is what it's all about.

As you can see from the data, no troubles or interference recording data with the cables plastic tied together. I recently corresponded with another Forum member from Colorado. He's running his skysreen cables for his Oehler 35P in one bundle and getting about 2-3fps differences between his primary and proof channel over a 6' long skyscreen separation distance with his 338 Lapua Improved. His ES is running less than 10 fps for his final loads. So with that kind of quality data, he's obviously not experiencing any problems with electrical interference.

I talked to Ken Oehler and his wife at the 2009 Shot Show in Orlando, Florida. They told me their current Skyscreen III units are better insulated compared to their prior generation skyscreens. He told me that the PACT skyscreen cables should not interfere with the Oehler skyscreen cables or operation. But I didn't ask either of them if they recommended bundling Oehler Skyscreen III generation cables together, or if that would be problematic.

Supporting your comments though, the PACT technician I talked with about 4-5 years ago via telephone told me that their skyscreen cables should be kept separated. I've always done that my PACT until I set up my new Oehler 35P on this newly constructed (homemade) skyscreen rail. I've only shot the initial bullets over it that I posted data for earlier in this thread. So far - so good. But I appreciate your observations and comments, and I will keep that in mind if the PACT starts to act up.

I never even used the Oehler-provided 4'-long piece of EMT skyscreen rail that was shipped out with their 35P, so I haven't really inspected it for straightness. The first bullets I fired over the 35P were over my homemade 6' 8"-long skyscreen rail. Also, I've never used any PACT provided skyscreen rail. I prefer to shoot over skyscreens separated over a 5 to 6 foot distance, in order to reduce the error associated with slightly inaccurate skyscreen separation distances.
I realized that you were using all the screens at the sametime after re-reading your post. Looks like your seeing about .25% just off the top of my head. I wonder what the built in error factor is for each unit? And with a 3600 fps round going thru there will you see a one quarter percent variation? (still less than 10fps). With the screens, I would be more concerned with the direction (s) the screens are pointed at than anything else, yet I think they'd still be good with a five degree variation at the max. Maybe I'm wrong, I don't know. I can tell you that when aligning light curtains (very similar concept), that they had to be pretty close. Still if the screens move from muszzle blast, you will induce a little error that can't be avoided. Your tests are interesting, and I'm following them.
gary
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  #16  
Old 10-17-2010, 07:29 PM
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Re: New Oehler 35P, New skyscreen rail, First Test Data

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Originally Posted by phorwath View Post
If I experience any troubles, I may send you a PM to inquire about these cables. I don't know what brand skyscreen cables Oehler is currently using. But there is some writing stamped on their cables. I'll take a look and see if the brand name of their Skyscreen III cable is legible.
I only know of one importer for Gronenberg cables, and he's in Indianapolis. The Lundberg cables are fairly common and can be bought from Kirby Risk and maybe Mosier. They are wrapped in silver foil with a nice flexable rubber coating. They come in all sorts of lengths, and are often seen with encoders and very low voltage aps. When you buy them they are normally terminated on one end to your specs (they sell about everykind of connector used including DIN couplings). They really shine in discrete applications where there's a lot of interference close by. Another good one is from TPC, and these can be had with about everykind of foil wrap out there.
gary
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  #17  
Old 10-17-2010, 10:12 PM
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Re: New Oehler 35P, New skyscreen rail, First Test Data

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Originally Posted by Trickymissfit View Post
I realized that you were using all the screens at the same time after re-reading your post. Looks like your seeing about .25% just off the top of my head. I wonder what the built in error factor is for each unit? And with a 3600 fps round going thru there will you see a one quarter percent variation? (still less than 10fps). With the screens, I would be more concerned with the direction (s) the screens are pointed at than anything else, yet I think they'd still be good with a five degree variation at the max. Maybe I'm wrong, I don't know. I can tell you that when aligning light curtains (very similar concept), that they had to be pretty close. Still if the screens move from muzzle blast, you will induce a little error that can't be avoided. Your tests are interesting, and I'm following them.
gary
The answer is yes, at MV of 3000 fps. I've been shooting over the Oehler 33 and PACT chronographs in tandem for several years now. The delta of the differences in velocity recorded over those two units is in the low single digits with MVs in the 2900-2950 fps range. So I am confident that the shot to shot precision of the combined units is normally less than 0.25% with MV less than 3000 fps. I have shot some strings in the past where the delta of the differences in recorded velocity is less than 2 fps. Most of the time (well more than 50% of the time) I'm getting deltas of less than 5 fps.
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  #18  
Old 10-17-2010, 10:17 PM
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Re: New Oehler 35P, New skyscreen rail, First Test Data

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Originally Posted by Trickymissfit View Post
I only know of one importer for Gronenberg cables, and he's in Indianapolis. The Lundberg cables are fairly common and can be bought from Kirby Risk and maybe Mosier. They are wrapped in silver foil with a nice flexible rubber coating. They come in all sorts of lengths, and are often seen with encoders and very low voltage apps. When you buy them they are normally terminated on one end to your specs (they sell about every kind of connector used including DIN couplings). They really shine in discrete applications where there's a lot of interference close by. Another good one is from TPC, and these can be had with about every kind of foil wrap out there.
gary
The Oehler Skyscreen III cables are marked with this identification:

C & M Corp AWM Style 2464 80C 300M VW-1 --- LL33361

They seem to do the trick.
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  #19  
Old 10-18-2010, 11:32 AM
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Re: New Oehler 35P, New skyscreen rail, First Test Data

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Originally Posted by phorwath View Post
The answer is yes, at MV of 3000 fps. I've been shooting over the Oehler 33 and PACT chronographs in tandem for several years now. The delta of the differences in velocity recorded over those two units is in the low single digits with MVs in the 2900-2950 fps range. So I am confident that the shot to shot precision of the combined units is normally less than 0.25% with MV less than 3000 fps. I have shot some strings in the past where the delta of the differences in recorded velocity is less than 2 fps. Most of the time (well more than 50% of the time) I'm getting deltas of less than 5 fps.
actually your results are slightly closer than what Doug and I found when compairing his #35 with the PACT. We would get a variation of about six to eight feet per second. But just as importantly the figures always paralleled each other. I have no idea how you would calibrate either one. Let alone what would you use for a master to go by
gary
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  #20  
Old 10-18-2010, 11:37 AM
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Re: New Oehler 35P, New skyscreen rail, First Test Data

Quote:
Originally Posted by phorwath View Post
The Oehler Skyscreen III cables are marked with this identification:

C & M Corp AWM Style 2464 80C 300M VW-1 --- LL33361

They seem to do the trick.
if they work well for you then so be it. What I'd like is a cable that detaches itself from the screens using a DIN connector (or something else). My big feet are hard on cables!
gary
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  #21  
Old 10-18-2010, 02:52 PM
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Re: New Oehler 35P, New skyscreen rail, First Test Data

Quote:
Originally Posted by Trickymissfit View Post
We would get a variation of about six to eight feet per second. But just as importantly the figures always paralleled each other. I have no idea how you would calibrate either one. Let alone what would you use for a master to go by.
gary
When I use the term 'delta of the differences', I am meaning 'paralleled each other'. That's the true reflection of the precision and repeatability of the chronograph setups. In other words, if I were to reset my skyscreen separation distances such that two units provided basically the same velocity (never being sure which velocity is closer to the true actual velocity), and then fired a string of bullets over the chronographs, the maximum difference between the recorded velocities is generally less than 5 fps.

As to determining which velocity of the four recorded velocities I receive from my chronograph setup is closest to the true bullet velocity (the most accurate - closest to the bullseye)? I rely on the three chronographed velocities from the units with the skyscreens with the largest separation distance. I measure and set the skyscreen separation distance as accurately as possible, and then look at the recorded velocities from the three units. In my initial test run using the new skyscreen rail, the two Oehlers with their 6' separation distance and the PACT with its 56" separation distance, were all in very close agreement. So I would average the three velocities, cross my fingers, and conclude that the average of the three is very close to the true bullet velocity. I don't know of any better way to go about it with the tools at my disposal. I don't claim to be able to know the absolute true velocity of my loads. I do claim to be able to determine the ES and SD of my loads to a very high level of accuracy and precision. And my gut feeling is the true bullet velocity isn't very far from the average of the three units.

It would be nice to transport my three units down to Oehler's factory and run them concurrently with one of their $15,000 units, or run them next to a radar set-up. Other than that, averaging the recorded velocity over multiple units is the best idea I've been able to come up with - so that's what I do.

Running multiple chronographs concurrently allows one to quantitatively identify the more reliable chronograph system from the less reliable chronograph system. I keep a running record of all of my shot strings on my PC. This is the process that allows me to state that my Oehler 33 is a more reliable unit with its Skyscreen IIIs - in fading light - than my PACT. Neither the Oehler 33 or the PACT are the current offerings from those two companies. In good lighting, the PACT operates just about as well as the Oehler 33. But I give the Oehler 33 the edge in performance because over the long haul, the ES produced by the Oehler 33 is generally 2-3 fps less than the ES recorded by the PACT. To me, this means the precision of the Oehler 33 is slightly better than the precision coming out of the PACT.

I haven't shot over the Oehler 35P other than the once - and I've posted that date in my initial Post. But over time, I will learn how it compares - performance wise - to the Oehler 33 and PACT.

Paul

Last edited by phorwath; 10-24-2010 at 02:57 PM.
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