Range Report Chronograph accuracy question

[ReaperDriver]

Yesterday while doing some load development alongside another Hide member (308Sako), we each had our chrono's set up. He has an Ohler 35 3-screen chrono with printer and I have my new CED M2. We were interested in a comparison to see how close together they read, so I moved my chrono to line up directly in front of his so each shot would pass through both in sequence. The center of the CED M2 was about 10' from the muzzle and the Ohler was about 15'. They were touching end to end.

Surprisingly, they read about 30-35' fps different BUT the the chrono in front (CED) read slower than the rear chrono (ohler). Both showed roughly the same difference shot to shot and roughly the same ES and SDs, so they were consistant there. I tend to believe the Ohler since it has 3 screens and is known to be more precise. Should I assume my CED is 30fps slow and add that to all my loads or is there another better way to check its accuracy?

 

[ssgp2]

Re: Chronograph accuracy question

Try it again with the CED in front

 

[ReaperDriver]

Re: Chronograph accuracy question

The CED <span style="font-style: italic">WAS </span>in front.

 

[BryanLitz]

Re: Chronograph accuracy question

Chronographs are extremely sensitive to screen separation. There are a couple possibilities for the mis-match in velocities:

1) The CED sensors may not have been pushed all the way on tight. This would have the effect of making the CED read slower. It would take about 1/4" of extra space between the sensors to result in 30 fps of error.

2) The Oehler screens may have been too close together.

The best way to minimize chrono error is to space out the screens as much as possible. A 1/16" error in screen spacing for screens separated by 8' causes much less error than 1/16" of error for screens separated by 2'. With the Oehler it's possible to space out the sensors with common electrical conduit and program the chrono accordingly. The CED isn't as easy to modify. I'm looking for a way to space out my CED screens farther. I think 1" square aluminum stock will work but I'm not sure yet. Also, I don't know if it's possible to program the unit with different screen spacings. Even if it's not, you can just multiply the output by an appropriate scale factor to get the real velocity. For example, if you mount the screens 8' apart, and the computer thinks they're 2' apart, just multiply the velocity reading by 4.

Longer screen spacings make chrono's less sensitive to small errors including those errors associated with lighting conditions.

-Bryan

 

[BLAWTON]

Re: Chronograph accuracy question

Now you need to test them both up against a PVM and see what the results are.

 

[dougm58]

Re: Chronograph accuracy question

Couple more things to test:
reverse the chronos so the CED is behind

Also, try it at different times of day and light intensity.

My Oehler was very sensitive to bright light, much more so than my CED is.

Both are adequate units, I always check my computed drop tables by actually shooting at the distances and usually find I'm not exact based on the chronographed velocity readings and drop tables derived from them

 

[The Mechanic]

Re: Chronograph accuracy question

Bryan I think your work is phenomenal you are defiantly the ballistic "GURU". Now for my question. since the screen measures from the center of the two screens, wouldn't you multiply by 1/2 the factor or length? Flame on as I haven't been in college for a while (20 years?) but having to correct and help my kids with everything up to calc.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body">Chronographs are extremely sensitive to screen separation. There are a couple possibilities for the mis-match in velocities:

1) The CED sensors may not have been pushed all the way on tight. This would have the effect of making the CED read slower. It would take about 1/4" of extra space between the sensors to result in 30 fps of error.

2) The Oehler screens may have been too close together.

The best way to minimize chrono error is to space out the screens as much as possible. A 1/16" error in screen spacing for screens separated by 8' causes much less error than 1/16" of error for screens separated by 2'. With the Oehler it's possible to space out the sensors with common electrical conduit and program the chrono accordingly. The CED isn't as easy to modify. I'm looking for a way to space out my CED screens farther. I think 1" square aluminum stock will work but I'm not sure yet. Also, I don't know if it's possible to program the unit with different screen spacings. Even if it's not, you can just multiply the output by an appropriate scale factor to get the real velocity. For example, if you mount the screens 8' apart, and the computer thinks they're 2' apart, just multiply the velocity reading by 4.

Longer screen spacings make chrono's less sensitive to small errors including those errors associated with lighting conditions.

-Bryan</div></div>

 

[BryanLitz]

Re: Chronograph accuracy question

M,

I'm not sure I follow. If you're talking about the Oehler with 3 screens, it has it's own internal adjustment for different screen spacings so no scale factor is necessary.

You would need the scale factor for the CED which only has two screens. The only way it can calculate speed is by dividing distance (ft) by time (seconds). It's using 2' as the distance and dividing that by the time between the start and stop signal. If you stretch the distance by 4 times without telling the computer, it will give you a velocity that's 1/4th what it should be.

I think we're on the same page, just mis-communicating here.

-Bryan

 

[ReaperDriver]

Re: Chronograph accuracy question

Bryan, Thanks as always. I'm usually pretty meticulous when I set up the unit, but I will try to pay more attention to whether the screens are pushed in all the way. It makes sense on that short a spacing that even a little error would be magnified. I thought all my loads that day were abnormally slow for what I was expecting and maybe that was the culprit.

I'm also interested to see if you get the CED working with a longer screen spacing.

FYI - it was an overcast day with no direct sun, but pleny of light being mid-morning/noon.

 

[308sako]

Re: Chronograph accuracy question

Deleted in protest!

 

[:X2:]

Re: Chronograph accuracy question

ReaperDriver
I did the exact same test as you when I bought my CED M2 , CED in front of an Oehler 35, with almost identical results. My CED was a about 40fps slower than the Oehler if memory severs me correct. What I did to the fix the problems was remove the sensors from each end of the 1” aluminum tubing, then remove the caps that covered the aluminum tubing, slipped the sensors back on, thus allowing the sensors to sit closer together since the caps on the aluminum added nearly 1/8” to each end. I did this while I was sit up in front of the Oehler so I could get the spacing of the CED sensors to read the same velocity as the Oehler. Once everything was locked down and at the correct spacing I took a sharpie and marked the sensors at both ends just encase they ever moved.

X2

 

[ReaperDriver]

Re: Chronograph accuracy question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: X2</div><div class="ubbcode-body">ReaperDriver
I did the exact same test as you when I bought my CED M2 , CED in front of an Oehler 35, with almost identical results. My CED was a about 40fps slower than the Oehler if memory severs me correct. What I did to the fix the problems was remove the sensors from each end of the 1” aluminum tubing, then remove the caps that covered the aluminum tubing, slipped the sensors back on, thus allowing the sensors to sit closer together since the caps on the aluminum added nearly 1/8” to each end. I did this while I was sit up in front of the Oehler so I could get the spacing of the CED sensors to read the same velocity as the Oehler. Once everything was locked down and at the correct spacing I took a sharpie and marked the sensors at both ends just encase they ever moved.

X2
</div></div>

COOL! I never thought to measure the actual distance when mounted on the bar - but did you measure the distance once you removed the caps? Are they now exactly two feet apart?

 

[:X2:]

Re: Chronograph accuracy question

Good question! I had to go measure it to find out and yes….right on the money. I’m guessing if I would have measured before I did the adjustment it would have been a hair long. I really wasn’t too worried about the exact distance as I knew the Oehler I was “tuning” it too was correct (the Oehler had been compared to other Oehlers, so I’ll consider it correct anyways).

X2

 

[ReaperDriver]

Re: Chronograph accuracy question

Sweet! Thats job #1 when I get home from work tonight. And then I get to settle in and load all my .308 rounds for my 1K desert shoot tomorrow. Looks like no sleep for me tonight

 

[CCooper]

Re: Chronograph accuracy question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: X2</div><div class="ubbcode-body">ReaperDriver
I did the exact same test as you when I bought my CED M2 , CED in front of an Oehler 35, with almost identical results. My CED was a about 40fps slower than the Oehler if memory severs me correct. What I did to the fix the problems was remove the sensors from each end of the 1” aluminum tubing, then remove the caps that covered the aluminum tubing, slipped the sensors back on, thus allowing the sensors to sit closer together since the caps on the aluminum added nearly 1/8” to each end. I did this while I was sit up in front of the Oehler so I could get the spacing of the CED sensors to read the same velocity as the Oehler. Once everything was locked down and at the correct spacing I took a sharpie and marked the sensors at both ends just encase they ever moved.

X2


X2, thanks for pointing this out. I would believe that CED would make sure their brackets are manufactured to space their sensors exactly 24" apart, but it seems this may not be the case. I measured mine and found that the sensors are 24 1/8" when they are pushed all the way in. This is measured from center to center of the sensors or front to front which is how I figure the sensors register the projectile. I'm going to call CED next week to verify where I should measure. I think without spending considerably more money, the CED M2 is the best, but it always seems that I have to add roughly 40-60fps to my velocities to make my known come-ups jive with what JBM is telling me. Was it fairly easy to remove the plastic caps from the end of the brackets X2? I will try later, but would like to be able to replace them easily if needed.

</div></div>

 

[ReaperDriver]

Re: Chronograph accuracy question

I'm really interested in what CED says about the measurement. Being 40-60 fps slow would explain not only why I don't jive with jbm but why I'm usually consistantly .2 mils high at 400 yds from what ballistic on my iPhone says.

 

[yotechsr]

Re: Chronograph accuracy question

Bryan, are you a berger rep or just a consultant?

 

[BryanLitz]

Re: Chronograph accuracy question

t,
I'm Berger's full time Chief Ballistician.
-Bryan

 

[ReaperDriver]

Re: Chronograph accuracy question

Well, I measured my screens on my CED M2 and they seem to be about as exactly 2ft apart as I can measure. Perhaps the last time I shot using it (I was in a hurry to setup), I didn't get the sensors pushed all the way onto the bar. I'll be dilligent next time and see if I get any different results. Maybe I can put it up against the Ohler again sometime soon.

As a related Q: you guys that are using the IR screens now - did you see any difference in velocities with the same load between using the IR screens and the original ones?

 

[338LM]

Re: Chronograph accuracy question

When I ran my original CED M2 screens mine were very sensitive to lighting conditions. I can't tell you how many times my data would vary for the same load 80% of the times that I went out and also in the same range session. It was a PITFA.

Bought the IR screens and rechargable battery pack. Simply an amazing difference. My velocity spreads and SD's were so tight through the range session that you would never believe it if I told you. And they do not vary at all between range sessions for the same load.
Hated to part with the money but it was definitely worth every penny spent.

 

[ReaperDriver]

Re: Chronograph accuracy question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 338LM</div><div class="ubbcode-body">When I ran my original CED M2 screens mine were very sensitive to lighting conditions. I can't tell you how many times my data would vary for the same load 80% of the times that I went out and also in the same range session. It was a PITFA.

Bought the IR screens and rechargable battery pack. Simply an amazing difference. My velocity spreads and SD's were so tight through the range session that you would never believe it if I told you. And they do not vary at all between range sessions for the same load.
Hated to part with the money but it was definitely worth every penny spent. </div></div>
damn you, you just cost me $150!

 

[memilanuk]

Re: Chronograph accuracy question

Bryan,

There should be a button top-dead-center of your keypad that says 'Screen 2 4 6 8'... at least there is on a CED Millenium (not M2).

The standard CED claim is that with the faster processor time of the new electronics in a CED unit that the extra distance doesn't help *that* much.

Years ago I did a test with two CED Milleniums... mine, and one belonging to a friend. Placed them end to end, then shot through them, swapped the controllers and did it again. One unit read consistently 23-24fps slower than the other regardless of how they were configured. That said... they tracked extremely closely - within 2-3fps of one another (taking that 23-24fps offset into account).

The thing that rubs me raw about the CED (or most chronographs) is that getting hard data on their test procedures or standards is like pulling teeth out of a chicken. RSI claims that info came from CED, who says that info came from some mystical German test lab... and no, they don't have copies for public consumption other than the 'doctored' version on the website. At least thats the song and dance I got.

Maybe with your 'pull' you could get some useful information and do a comparison?

Monte

 

[Mag 300]

Re: Chronograph accuracy question

2-3 fps spread is unreally close !!!!
used to 20 fps plus with meticulously loaded rounds.
Nice!!!

 

[Greg Langelius *]

Re: Chronograph accuracy question

Did much the same as you with three chronos in line starting about 20' out to minimize the potential for velocities being fudged by muzzle blast.

Same results, same variations, different velocities.

This is why I don't pay much attention to Chrono data anymore, except as a ballpark guide to determining overall hopefully-on-paper starting zeroes.

I think that when I read instructions that specify an average error rate of about +/-1% of reported velocity, it becomes overly optimistic to base claims of single (and possibly even double) digit ES/SD numbers, etc., when any and probably all of the numbers used for the computation could be off by as much as 30fps over or under what's reported when the base speed is around 3000fps. Even at their best, they're just not accurate enough for a lot of the beliefs people place in what the machine is reporting.

My chrono is the target. At least I know I can trust <span style="font-style: italic">that</span>.

Greg

 

[BryanLitz]

Re: Chronograph accuracy question

Monte & Greg & all,

We all share your frustrations. Chronographs are important instruments for what we do and it's very difficult to get a unit that you can really have (well informed) confidence in.

My CED M2 doesn't have the button for screen spacing as you described. There is a button that has 'SP' on it which will probably allow me to program it for a different spacing. Guess I have to dig for the manual.

When I first got the CED I did an in-line comparison with my Oehler (8' spacing) and they matched very well. I was using 25 caliber bullets in ideal light conditions. Later when using just the CED in poor light conditions with .224 caliber 90 grain VLD's (a difficult bullet for the optical sensors to trigger consistently) I had some erratic velocities which, combined with my tof measurements resulted in some rather inconsistent BC results.

CED/RSI may claim that the super-duper fast clock in the unit negates the advantage of a longer screen spacing. That may be true if you only consider the theoretical resolution based on clock speed, but in the real world, <span style="text-decoration: underline">there's a lot of error that comes from how consistently those sensors trigger</span>. Poor light conditions and long pointy bullets will challenge the consistency of those sensors. If you separate the sensors by more distance, it cuts down on the error. It's measurement uncertainty 101, and it's not just academic. Greater screen spacing has been shown to produce more consistent velocity measurements under all lighting conditions when compared in deliberate tests.

I also suspect that chronographs can be very affected by the life in the battery. They'll continue to 'work', with a higher failure rate and more erratic velocities all the way till the battery's dead; but I *think* they work much better (more reliable and accurate) with fresh new batteries. Take this with a grain of salt because it's based on very few data points.

When the time is right in the cash flow, I'm going to have a PVM. I'm a strong believer in the old adage: "You get what you pay for" and the PVM's are the spendiest units available.

There's a rumor that Paul McMinimain (web master of 6mmBR.com) has done a comparison of all available chronographs including Chrony, Pact, CED, Oehler, and *PVM*. His focus was mostly features and reliability, not so much focused on accuracy, but I'm sure the results will indicate something.

How 'bout it? Anyone have experience with the PVM? It is a short unit, which makes me nervous, but if the sensors are much more reliable than conventional optical sensors, they might get away with it.

-Bryan

 

[James in Wyoming]

Re: Chronograph accuracy question

See my posts on the "PVM group buy" thread. I will say that the PVM seems to give a reading in a much larger range of light conditions than all the others out there. Confidence in the readings, however, is another matter. The issues I have been having with one or two "wild" (i.e. more than 100fps) readings in a string of 15 or so have been with a couple of .338 Lapuas, braked. The unit is more consistent with smaller calibers and no brakes, but still has issues for field use. Spoke at length with Ed at Neco yesterday looking for a solution. In addition to experimenting with the gain function and the distance of the screens from the muzzle, he suggested I epoxy the connections into the screen units to eliminate wiggle and vibration and further suggested that wind, especially at vectors close to 1200 and 6 o'clock to the screens, could account for the occasional erratic reading. I had to chuckle as wind of some sort is a pretty constant factor for me here in Wyoming, but this was not what I wanted to hear. I really don't care about a direct computer interface; I want consistent reliable results in the field at the time of shooting and am not convinced that's what I'm getting from the PVM. This unit was designed by indoor smallbore shooters, no doubt its one of the more sophisticated sensors on the market, but it has real issues for those of us who shoot outdoors any/all conditions, occasionally with calibers/brakes which induce some substantial muzzle blast. I like the fact that i can almost always get a velocity reading; the question is how believable are the results?
Best,
James

 

[Greg Langelius *]

Re: Chronograph accuracy question

Bryan;

Thank you very much for your info, as always (and James as well, our posts crossed).

I have limits on my reliances of numbers and calculations. Experience has shown that they can tell much, and what they tell is very useful, but they do not tell all; and in the end, one simply has to get out there and do battle with the reality and the elements which inhabit that reality.

The gun is gonna do what the gun does and if the calcs say otherwise, I'm gonna believe the gun.

It's not that the calcs are unreliable, it's that they usually omit significant details about conditions along the trajectory arc. Consistency and reality seldom co-exist. The details are generally not measurable; or if they are, the processes of inputting the data and performing the calculations are so time consuming that either way, they no longer reflect the true reality of the conditions affecting the outcome of the shot next.

Maybe means of instrumentation and data acquisition exist that negate this thinking, I honestly don't know. But I think we still have a way to go before calcs and outcomes synchromize reliably. I think radar will figure strongly in that success.

Greg

 

[kmussack]

Re: Chronograph accuracy question

I used to think that measuring velocity was critically important.

However, I now see the entire exercise as being almost irrelevant.

I load my ammunition to be safe from a pressure perspective and as accurate as necessary. I no longer worship at the altar of velocity.

Once I get accurate reliable ammunition I use my ballistic software to grind out data that matches my empirical data. I do this by tweeking the BC and muzzle velocity inputs.

What’s the actual velocity? I don’t care so long as I can resolve an effective firing solution.

Oh, I’ll still shoot my loads over my chronograph to get a starting number and besides it makes me look all “high speed/low drag” at the local gun club.

 

[goober]

Re: Chronograph accuracy question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kmussack</div><div class="ubbcode-body">I used to think that measuring velocity was critically important.

However, I now see the entire exercise as being almost irrelevant.

I load my ammunition to be safe from a pressure perspective and as accurate as necessary. I no longer worship at the altar of velocity.

Once I get accurate reliable ammunition I use my ballistic software to grind out data that matches my empirical data. I do this by tweeking the BC and muzzle velocity inputs.

What’s the actual velocity? I don’t care so long as I can resolve an effective firing solution.

Oh, I’ll still shoot my loads over my chronograph to get a starting number and besides it makes me look all “high speed/low drag” at the local gun club.
</div></div>

What distance do you start with when no using the chrony ? I generally can stick more pills through the centre at 300 yards than not with a 3inch bull and is from there i will start again as I am developing a new load right now .I was using my employers chrony but shot it some time back so bought him a brand new one -sadly while out testing today the second shot to bring the scope to zero wasnt quite correct and I will be purchasing the boss a third chrony !!!gota love Xmas yo ho ho sobbing

 

[Tribe]

Re: Chronograph accuracy question

dude.

 

[ReaperDriver]

Re: Chronograph accuracy question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tribe</div><div class="ubbcode-body">dude. </div></div>

Wow. Note to self.... zero the rifle FIRST and <span style="font-style: italic">THEN </span> use the chono.

 

[goober]

Re: Chronograph accuracy question

ass was kicked alway home and dropped into chemist for pills to cure my fuckwititis. thought I had zeroes the scope visually -the joys of not having a zero stop huh.

 

[rocdoc]

Re: Chronograph accuracy question

so is there a chronograph make/model that is considered to be the most accurate/reliable?

 

[Brians708]

Re: Chronograph accuracy question

ROCDOC,
All of em work for the most part. Some folks have quality issues from year to year with the cheaper models. The Oehler has been the boss for many years with the folks I know. I have heard good things about the CED's as of late but I have not used one yet. Recently I picked up a CHRONY ($150) and its cheesy compared to the Oehler I usually barrow. But it works for getting gross numbers and setting me in the right direction- which is all I am looking for.....it would take the fun out of it if the thing ran like an auto-pilot

 

[Lumpy Grits]

Re: Chronograph accuracy question

Hi, when I start a crono session I will ALWAYS use fresh batts.
It does make a diff.
Respectfully,
LG

 

[ReaperDriver]

Re: Chronograph accuracy question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: lumpy grits</div><div class="ubbcode-body">Hi, when I start a crono session I will ALWAYS use fresh batts.
It does make a diff.
Respectfully,
LG </div></div>

My batts died at the end of my last range session (the one where I compared to the Ohler). I wonder if that might have been part of the issue with the discrepancy in velocities???

 

[Lumpy Grits]

Re: Chronograph accuracy question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: lumpy grits</div><div class="ubbcode-body">Hi, when I start a crono session I will ALWAYS use fresh batts.
It does make a diff.
Respectfully,
LG </div></div>

My batts died at the end of my last range session (the one where I compared to the Ohler). I wonder if that might have been part of the issue with the discrepancy in velocities??? </div></div>

Hell YES!

 

[rocdoc]

Re: Chronograph accuracy question

since the oehler is no longer available (new), how does the Pact xp pro stack up against the CED m2? I like the fact the Pact has a printer built in...

 

[ReaperDriver]

Re: Chronograph accuracy question

Well... good news with the Chrono today. I snuck out for a quick session to chrono some loads that seemed to be shooting accurately. So I was extra careful to make sure the sensors were all the way on the bars and I put a fresh battery in bought at the store about 30 min before.

I shot several of my loads that seemed a bit slow on the previous session and they were a bit quicker this time (about 20-25fps) but still a hair slower than I would have liked. BUT.... another guy that had chrono'd his loads across the Ohler 35P mentioned previously was also there today and I talked him into shooting a few of his known loads with his rifle across my chrono so I could see if it was reading accurately. He said he got just a hair over 2700 fps with his 44.4 Varget, lapua and 175 SMK load. Sure enough, he shot three across my CED M2 and he averaged 2710. So its right on the money with what was expected. So that's given me a bit more confidence in the data.

The bad news is that means my gun is much SLOWER compared to his than I would ahve expected. He is shooting a 22" Bartlein tight bore and I'm shooting out of my factory Rem 700 SPS_T 20". based on barrel length alone, I would have expected him to be about 50fps faster, but I'm running about 140-150 fps slower in my gun with the exact same load and components. Its amazing that a tight match chamber can add an additional 100fps MV.

 

[CCooper]

Re: Chronograph accuracy question

I spoke to the owner of CED (Charles Hardy) about this. He spoke with one of the engineers about the spacing of the sensors on the bracket. The engineer responded that the sensors need to be precisely 24" apart as that is what the calculations are based on. I told him my sensor eyes are 24 1/8" apart center to center or first edge to first edge (same distance). He is sending me a replacement bracket to see if I get exactly 24" after using the new bracket. I'll let yall know what the results are.


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body">I'm really interested in what CED says about the measurement. Being 40-60 fps slow would explain not only why I don't jive with jbm but why I'm usually consistantly .2 mils high at 400 yds from what ballistic on my iPhone says. </div></div>

 

[problemchild]

Re: Chronograph accuracy question

I have noticed things that run on battery can be off more than 110v things.

 

[Lumpy Grits]

Re: Chronograph accuracy question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: problemchild</div><div class="ubbcode-body">I have noticed things that run on battery can be off more than 110v things. </div></div>

HUH?
How many shooting ranges do you know that have 110v/ac at the benches?
Please name the "hobby-type" cronographs that you know that run on 110v/ac?
Respectfully,
LG

 

[azimutha]

Re: Chronograph accuracy question

I'm wondering a couple of things regarding these units. Last fall, I creased the top of my CE ProChrono right above the rear sensor. I took it apart at home and got everything back together. However, last time at the range, it was very inconsistent. I noticed that their operating temperatures bottom out at 32F and it was around 25F that day...not sure why that would matter. I will also try a brand new battery next time out before replacing the unit. I don't mind sticking in a new 9v every time because they can always go into a smoke detector or similar afterwards.

If I do get a new one, looks like the best choices are the ProChrono or the CED M2. I'm not thrilled about spending extra on the IR screens though.

 

[19Scout77]

Re: Chronograph accuracy question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body"> The bad news is that means my gun is much SLOWER compared to his than I would ahve expected. He is shooting a 22" Bartlein tight bore and I'm shooting out of my factory Rem 700 SPS_T 20". based on barrel length alone, I would have expected him to be about 50fps faster, but I'm running about 140-150 fps slower in my gun with the exact same load and components. Its amazing that a tight match chamber can add an additional 100fps MV. </div></div>

I think you will find that, with only rare exceptions Bartlein and other well made custom barrels shoot ALOT faster than factory barrels. I know of one instance in which a 22" Bartlein shot faster than a 26" Sako TRG, all other things being equal.

 

[Tribe]

Re: Chronograph accuracy question

FWIW.... tried old vs new batteries on a couple of Chronos recently... no difference in results during the same range day.

However, seems like every time I go out, the chrono, although consistant, will read relatively significant differences in velocities from one session to another... same load, similar temp... just different day. Lighting would be the best guess I have for variences. But yeah, two units end to end... 50fps apart. After a great deal of chasing that rabbit down the hole, I have decided it's good for horse shoes & hand grenades, but in the end, I've concluded the best method, is simply to "Believe the bullet"...as Lowlight, Jacob and others no doubt, are always preaching....

 

[Short-bus]

Re: Chronograph accuracy question

The more that I shoot over my chrony, the more I start to think about just selling it, and using range derived data to determine/proof my loads. I have access to long range, so shooting at 600 yards to see if I have good vertical dispersion is doable. Couple that with logging my come ups, and conditions, I can derive my velocities.

For the ballpark figures, I suppose it's a good idea to have one. I'd really hate to develop a load and it shoot really good, but find it's 200fps slower than the target velocity that i'm shooting for. This was the case not long ago when I was developing my 208amax, I got some stellar groups at the low end, but the velocity was only like 2300fps, target minimum was 2500. It would stink to take that load out to 600 and find that's the case, and have to return to square 1 and step up.

Branden

 

[Unsichtbar]

Re: Chronograph accuracy question

I just had a real odd set of results from two chronograph trips to the range. I was using a CED that I have had for years. Well the loads that I had chronographed were about 100 ft slower than the first range session all of the rounds about a 100fps off. I checked everything and could not figure it out.

I think what happened is the second session I shot prone instead of off a bench, I had to angle the first screen lower than the second screen since the target was elevated. That was enough induce more length because of the angle, than the 48" spreader bar being level, the longer distance threw the readings way off I think.

 

[Lumpy Grits]

Re: Chronograph accuracy question

What was your temp & RH diffs. between the 2 sessions?
Respectfully,
LG

 

[Mag 300]

Re: Chronograph accuracy question

Hard to tell accuracy / measurement differences but the temp and altitude will do it. problem is how do you tell?????
Bill

 

[Tribe]

Re: Chronograph accuracy question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Unsichtbar</div><div class="ubbcode-body">I just had a real odd set of results from two chronograph trips to the range. I was using a CED that I have had for years. Well the loads that I had chronographed were about 100 ft slower than the first range session all of the rounds about a 100fps off. I checked everything and could not figure it out.

I think what happened is the second session I shot prone instead of off a bench, I had to angle the first screen lower than the second screen since the target was elevated. That was enough induce more length because of the angle, than the 48" spreader bar being level, the longer distance threw the readings way off I think.
</div></div>

If the readings are EXTREMELY sensitive to level.... that would explain a lot.....