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

[Pdvdh]

the differences between all the units is nil at best. But I gotta ask you one question; I see that you have the screens setup at 34 feet from the muzzle. Any particular reason why?
gary

Hi Gary,
As I was typing that information, I was wondering if it wouldn't prompt the question. No scientific reason was involved. The only reason I placed the skyscreen rail that far from my muzzle was due to the ground surface terrain/elevation where I set up to shoot. The local range where I normally shoot out to 300 yards has been closed to access for quite some time now. So I had to improvise and locate a suitable 'range' on a power line clearing with a downrange hillside for a safe bullet backstop. It was simply that the topographic relief where I set up required that the tripod and skyscreen rail be that far in front of the muzzle in order to get the correct bullet-above-skyscreen separation distance.

I normally set the first skyscreen up about 15 feet off the muzzle - or as far as the cables will reach from the three chronograph computer units. And I haven't experienced any muzzle blast-related problems with the skyscreens placed 15 feet ahead of the muzzle. This time I had to get up from the prone position after each shot and walk out to retrieve and record all the data from the three chrono units. Not really a problem since there I was out in the boonies all by my lonesome - no other shooters around. Some brown bear tracks up and down the power line though! Another good reason to get up and look around after every shot fired!!!

I agree that the differences between the three units on this outing is for all intents and purposes - negligible. I don't plan on tweaking any of the skyscreen separation distances. Now that I know that the one channel reads a couple fps faster than the other three, as long as I experience that on all the shots fired, I'll know the data is completely proper - based on the existing skyscreen separation distances.

Cheers,
Paul

 

[Mikecr]

It looks like you've chosen the combo O33/pact readings as a 'standard' which you're calibrating the O35P to. But what I wonder is, are you sure ANY of these are right?
Afterall, you wouldn't want to calibrate these all to a wrong standard.

Have you adjusted these chrono velocities to muzzle velocities?
MV = e(chrono distance / Bullet BC/ 8816 ) x Chrono Velocity
This is EXP(number), the exponent applied to the base 'e'
So with these terms:
34' chrono trigger to muzzle
.700 BC
3050fps chrono reading
EXP(34/.700/8816)*3050 = 3067fps MV

Just a reminder, before applying this data toward ballistic solutions.

 

[Trickymissfit]

Hi Gary,
As I was typing that information, I was wondering if it wouldn't prompt the question. No scientific reason was involved. The only reason I placed the skyscreen rail that far from my muzzle was due to the ground surface terrain/elevation where I set up to shoot. The local range where I normally shoot out to 300 yards has been closed to access for quite some time now. So I had to improvise and locate a suitable 'range' on a power line clearing with a downrange hillside for a safe bullet backstop. It was simply that the topographic relief where I set up required that the tripod and skyscreen rail be that far in front of the muzzle in order to get the correct bullet-above-skyscreen separation distance.

I normally set the first skyscreen up about 15 feet off the muzzle - or as far as the cables will reach from the three chronograph computer units. And I haven't experienced any muzzle blast-related problems with the skyscreens placed 15 feet ahead of the muzzle. This time I had to get up from the prone position after each shot and walk out to retrieve and record all the data from the three chrono units. Not really a problem since there I was out in the boonies all by my lonesome - no other shooters around. Some brown bear tracks up and down the power line though! Another good reason to get up and look around after every shot fired!!!

I agree that the differences between the three units on this outing is for all intents and purposes - negligible. I don't plan on tweaking any of the skyscreen separation distances. Now that I know that the one channel reads a couple fps faster than the other three, as long as I experience that on all the shots fired, I'll know the data is completely proper - based on the existing skyscreen separation distances.

Cheers,
Paul

well I think your tests were very complete, if that matters. Also the distance is not all that critical as along as you are the one using it for reference. The results pretty much compair to what Doug and I found with his #35 and my PC2. Kinda thinking about getting a new one, but then again what for? What I'd really like, would be a chronograph that you could simply stick an SD card into it, and later down load the data in your home PC.
gary

 

[Pdvdh]

It looks like you've chosen the combo O33/pact readings as a 'standard' which you're calibrating the O35P to. But what I wonder is, are you sure ANY of these are right?

After all, you wouldn't want to calibrate these all to a wrong standard.

I've thought about that Mike, and without having a certified, calibrated unit of some sort that's already been proven to read the exactly correct velocities, I was left with the next best option I could think of. Carefully establish the spacing of all seven skyscreens on my skyscreen rail to the separation distances programmed in each chronograph, and then shoot some bullets over them.

If I received some vastly differing velocities, I'd have the conundrum that you speak of. Which is how do I know which chronograph is recording the most correct - the most true - velocity?

On the other hand, if all three chronographs are in very close agreement, then I could reasonably conclude, based on the weight of the evidence, that my velocity data is very close to the true bullet velocities. Fortunately, this was the case. The Oehler 33 and the PACT were basically providing the same exact velocities. And the Oehler 35P was providing velocities very close to the 33 and the PACT. The only real adjustments I've made to the skyscreen spacings were with the Oehler 35P, and that was primarily to get the Proof Channel reading the same as the Primary Channel.

Don't get me wrong. I would love to be able to set these up alongside a Doppler Radar unit that's been Certified by NASA or Oehler to be dead nutz on the money. Then I could, and would, calibrate my skyscreen spacings to produce velocities that exactly match those known, true, bullet velocities. But without access to any calibrated and certified instrument, I did the best I could with the equipment I have available.

I'm unaware of any better options for the typical LRH. No one will ever convince me that their careful measurement of down range bullet drops will provide them more accurate muzzle velocities than I obtain with this multiple chronograph setup.

Corroborating evidence that my MV data is close to the true bullet MV is that when I shoot at 1000 yard ranges using my MVs, Bryan Litz's Berger VLD G7 BCs, and LoadBase 3.0 Ballistic Software, that my bullet drops are right on the money. The difference with my bullet drop measurement process is that I'm not using bullet drops to establish muzzle velocity for use in the ballistic software. I'm only using bullet drops to corroborate what I believe are accurate MV data obtained from the triplicate chronographs.

But I'm all ears, receptive - even eager - to receive any advice that could improve my calibration process.

 

[Pdvdh]

Have you adjusted these chrono velocities to muzzle velocities?
MV = e(chrono distance / Bullet BC/ 8816 ) x Chrono Velocity
This is EXP(number), the exponent applied to the base 'e'
So with these terms:
34' chrono trigger to muzzle
.700 BC
3050fps chrono reading
EXP(34/.700/8816)*3050 = 3067fps MV

Just a reminder, before applying this data toward ballistic solutions.

The velocities I posted were the data exactly as recorded by the three different chronographs. Your reminder is a good one, and I do convert/correct these data for velocity "at the muzzle". I use LoadBase 3.0 ballistic software to back calculate the actual bullet velocity at the muzzle of my rifle barrel.
Paul

 

[Trickymissfit]

I've thought about that Mike, and without having a certified, calibrated unit of some sort that's already been proven to read the exactly correct velocities, I was left with the next best option I could think of. Carefully establish the spacing of all seven skyscreens on my skyscreen rail to the separation distances programmed in each chronograph, and then shoot some bullets over them.

If I received some vastly differing velocities, I'd have the conundrum that you speak of. Which is how do I know which chronograph is recording the most correct - the most true - velocity?

On the other hand, if all three chronographs are in very close agreement, then I could reasonably conclude, based on the weight of the evidence, that my velocity data is very close to the true bullet velocities. Fortunately, this was the case. The Oehler 33 and the PACT were basically providing the same exact velocities. And the Oehler 35P was providing velocities very close to the 33 and the PACT. The only real adjustments I've made to the skyscreen spacings were with the Oehler 35P, and that was primarily to get the Proof Channel reading the same as the Primary Channel.

Don't get me wrong. I would love to be able to set these up alongside a Doppler Radar unit that's been Certified by NASA or Oehler to be dead nutz on the money. Then I could, and would, calibrate my skyscreen spacings to produce velocities that exactly match those known, true, bullet velocities. But without access to any calibrated and certified instrument, I did the best I could with the equipment I have available.

I'm unaware of any better options for the typical LRH. No one will ever convince me that their careful measurement of down range bullet drops will provide them more accurate muzzle velocities than I obtain with this multiple chronograph setup.

Corroborating evidence that my MV data is close to the true bullet MV is that when I shoot at 1000 yard ranges using my MVs, Bryan Litz's Berger VLD G7 BCs, and LoadBase 3.0 Ballistic Software, that my bullet drops are right on the money. The difference with my bullet drop measurement process is that I'm not using bullet drops to establish muzzle velocity for use in the ballistic software. I'm only using bullet drops to corroborate what I believe are accurate MV data obtained from the triplicate chronographs.

But I'm all ears, receptive - even eager - to receive any advice that could improve my calibration process.

I know this is gonna sound extremely nuts, but you might want to setup one more time, and try this. Find somebody that's got a mint Winchester 52D or a Remington 541S single shot rifle you can borrow. Get your hands on a box of Federal Olympic Gold ammo, and see what you get. This ammo is extremely close to the advertised velocities, and is probably the best quality ammo money can buy in just about any preloaded ammo of any caliber. A buddy of mine bought a brick of it ($$) to shoot in competetion, and shot about forty rounds thru my chronograph. The rounds varied something like six or seven fps, and were virtually dead on the advertised velocties with a 24" barrel (he was using a Cooper with a Krieger barrel that had a 52D chamber reamed in it).

As for proving your tests out, the only other way would be to have three or more Ohler 35's setup exactly the same way (normal testing requires three gauge to prove out the fourth one in a lab). Myself I'm quite satisfied
gary

 

[Pdvdh]

Some 985 Yard Data & G7 BC Determination

Another data set to digest. I shot @ 985 yards last weekend and was able to place some bullets over the skyscreens. I shot five times and received data on four of those five shots.

One shot passed wide and resulted in no velocity data.

I received partial data on shot #2, which passed slightly wide of the center line of the skyscreens. This likely caused a 20-21 feet/sec difference in the velocities recorded on the Oehler 33 and Oehler 35P, and no reading from the PACT. I conclude that chronographs are less likely to provide accurate data when the bullets aren't centered over the skyscreens.

The other three shots were dead center over the skyscreens. On shot #4, the last shot of the day, the light was fading and the PACT failed to record any velocity. I've experienced this several times over the past three years. The Oehlers continue to record velocity a bit longer than the PACT in fading light.

Here's the data I collected:

Shot . Oehler 33 . . Oehler 35Primary . . Oehler 35Proof . . PACT PC2
. 1 . . 1618 . . . . . . 1619 . . . . . . . . . . .1620 . . . . . . . . 1617
. 2 . . 1670 . . . . . . 1649. . . . . . . . . . 1651 . . . . . . . . .-NR-. . . . Poor agreement from the Oehlers. No reading from PACT. Discard these data.
. 3 . . 1627 . . . . . . 1630 . . . . . . . . . . .1627 . . . . . . . . 1630
. 4 . . 1638 . . . . . . 1642 . . . . . . . . . . .1640 . . . . . . . . -NR-. . . . No reading from PACT due to low light conditions.
Avg. . 1628 . . . . . . 1630 . . . . . . . . . . .1629

I had already determined the average Muzzle Velocity of this load at 3074 fps. The primary purpose of this chronograph session was to establish an accurate BC value for this bullet by obtaining 985 yard velocity data. Other reasons were to record 985 yard drops and accuracy.

Shot #2 yielded poor agreement between the Oehler 33 and the Oehler 35P, and no reading from the PACT. When I'm getting good data, the velocities will record within 5 feet/sec. Often within 2 or 3 feet/sec. So I didn't include shot #2 velocity data while determining my average 985 yard velocity. And since the PACT only recorded two velocities I chose to only use the bolded values from the Oehlers to calculate average V985s. I then used the average of these 3 average velocity values - 1629 fps - as my average 985 yard velocity. I used LoadBase 3.0 ballistic software to calculate a G7 BC value of 0.289. This G7 value is referenced to ICAO environmental conditions: 29.92 inches/Hg, 59F, and 0%RH.

LRH Forum member 'elkoholic' manufactured these bullets. He had determined a G7 BC value of 0.308, but his value was obtained from measured drops while shooting at an elevation of 2500 feet. So out of curiosity, I used LoadBase 3.0 to calculate a 985 yard velocity at the 2500 foot elevation, and then determined a G7 BC value of 0.311 based on that higher downrange velocity. Very close to the 0.308 G7 elkaholic had determined through measurement of downrange drops. elkaholic has probably shot and measured a lot of downrange drops.

These 190 grain SXRs are the most accurate bullets I've ever shot out of my 300 Win Mag. My very first load is providing significantly better accuracy than I've ever obtained with Berger 210 VLDs - even after extensive VLD load development efforts.

 

[Eaglet]

PHorwath,

Excellent! Well done!

I think we need to be friends

Wait, you're in Alaska right? Never mind! Just kidding buddy, you're my friend!!

 

[Broz]

Nicely done Phorwath. I appreciate your time and effort here. I am looking to buy a 35 P. You have restored some confidence with me as far as accuracy and consistancy in chrono's. Plus it seems one needs to be aware of where the bullets are under the screens and the amount of light at time of fire.

Thanks

Jeff

 

[Pdvdh]

Re: Some 985 Yard Data & G7 BC Determination

Thanks guys. I share this information with the hope that it is helpful. I'm learning more about chronographs with each data set myself. Every time a recording session provides a shot with disagreement between the chronographed velocities, I think back to when I was only using a single chronograph and had no way to identify the questionable data. And I wonder if I've discarded loads with high ES and SD values because of one bogus recorded velocity.

The Oehler 35P is unique in that it's basically the equivalent of two chronographs packed into one unit - having the primary channel - plus the proof channel. The primary channel should be expected to be the more accurate of the two over the long haul, since the Primary channel skyscreens are separated exactly twice the distance apart as the Proof channel skyscreens. The fact that you get two velocities recorded with the 35P for each bullet fired is a really valuable benefit. When both channels are in agreement, you can be fairly confident the data are accurate/good.

I debated whether or not to include the 35P data from shot #2 in my average velocity calculation. The 35P data were in excellent agreement, so those data might have been true and accurate. But they were higher than the rest, and the 33 velocity was out of whack in comparison. Plus the PACT didn't record. So I concluded the data were of dubious quality and didn't use them for my average V985 determination.

Broz, you shoot a lot. So much that you can probably develop really accurate drops over time and likely come very close to a reasonably correct MV by back-calculating with a ballistics program. Plus if you stick with the Berger bullets, Bryan has already provided accurate BCs. The bullet I'm using now hasn't been tested to determine a velocity-based BC by Bryan or anyone other than me, to my knowledge. In addition, I don't shoot nearly as much as you, so I don't develop confidence in my measured drops the way you can with extensive shooting over loooong distance. To make matters worse, I hunt at widely varying elevations and environmental/atmospheric conditions. Up and down the mountains at various elevations. It's common, perhaps even normal, for me to engage game over sloped ground in the 15-20 degree range. One fall we took a Billy goat over a 30-degree inclined slope at 720 yards. 30-degrees doesn't sound like a lot - but it looks like alot when you're in it! Because the mountainous country I hunt in provides such variable 'environmentals' and angled shots, I find comfort in tying down the bullet BC value as accurately as possible. Then I let Loadbase 3.0 determine the corrective dope for these variable conditions and I find that LB 3.0 provides very accurate predictive dope - under all the circumstances I've experienced to date. As far as recommending a chronograph: as serious as you are about your shooting, I endorse the 35P as a quality unit, with the HUGE benefit of providing a 2nd recorded velocity for each and every shot fired.

Hi Eaglet... Good to see you're making time to browse the LRH Forums and remaining engaged in our common hobby!

 

[elkaholic]

Great job Paul! It is very nice to get some data other than my own CRUDE stuff. I respect your work and I think you will REALLY appreciate the terminal performance of these bullets as well. Feel free to post any and all results, good or bad, so I can continue to improve on my design. You may include the expanded bullet pics if you like......Rich

 

[coues7]

Now that is a serious setup. Way to go. I have the new 35P and they are awesome.

 

[Eaglet]

Re: Some 985 Yard Data & G7 BC Determination

Hi Eaglet... Good to see you're making time to browse the LRH Forums and remaining engaged in our common hobby!

Yep! Just too many good folks sharing great info. I've got to hang around!

I see the awesome benefit of one chronograph giving too readings, nice.

I have two chronographs and you finally got my peanut brains into thinking about doing something about it. Once I had used them in tandem... Just once! I'm afraid that's about to change...

 

[Broz]

Hey Paul, I was at the shoot today and a friend had his Oehler 35P. He offer the use of it to me. I tested my .338 LM and 300 WM.

It printed off two velocities for each shot but they were different by about 20 fps. the first number was always the highest.

Conditions were 72 bright sun. First screen was 13' 6" from the muzzle. Shots were placed to be centered over photo cells and alinged perfect in the lower 1/2 of the "V"

Is this normal?

Jeff