Confused! chrony troubles

[Ksmirk]

Evening fella's I've got a "thing" going on a I'm scratching my head! wondering if any of you have run into this before so thought I'd just ask and see if you have any thoughts.

New rifle and working up loads, won't get into the caliber yada yada but the other day my brother and I had the rifle out for it's first run and used his Magneeto speed crony and we were getting some rather impressive velocities!

80.5 = 3036fps
81.0 = 3049fps
81.5 = 3065fps

I'm loading rather long with this caliber and well wanted to do some more testing as I thought the readings were a touch flakey! but hey stranger things have happened so I did another test with the same loads but this time I used my CED M2 crony and here's what I found,

80.5 = 2931fps
81.0 = 2967fps
81.5 = 2998fps

Now I've been using the CED M2 for many years and haven't had any issues when working up drop charts but I've got to admit now that I'm a touch confused as there is a good amount of difference between the two! none of the loads showed pressure sign BUT from what I've read I should be seeing some pressure around the 3050fps mark but which data do I use? I don't have another crony that I can use to verify and it's going to be a month before I can get to the range with enough distance to verify so I'm torn on what to do now and just wondering if any of you have run into this before and what you did? I appreciate any direction or thoughts but I'm about to the point of pulling my hair out trying to wrap my head around this one and none of the guys around here that I know have run into this issue so the reason I ask the folks of the inter webs. Thanks in advance!

 

[Ledd Slinger]

Magnetospeed sits right at the muzzle and the CED is farther away in front of the muzzle. Granted the speeds seem a little far apart for that much of a difference.

Those two chronographs use completely different technologies as well. Hard to say which is more accurate on the true speed.

However, it's obvious you are shooting a large magnum caliber (probably a bullet of 200gr or more) and judging by the powder charges and difference in speeds over the spread of 1 full grain, I would say the CED is giving you a more accurate reading if your brass is not showing high pressure signs. The CED is showing a gain of 67 fps with a full grain increase in powder, the Magnetospeed is only showing a 29 fps gain. Of course I'm not sure what the deviation will be on those loads, but if you are only getting 29 fps gain with a full grain increse in charge weight, that would indicate you are at max pressure. The CED is showing that max pressure has not yet been reached as is also indicated by your brass.

Personally, I wouldnt use a magnetospeed if it was given to me for free...

 

[Twoboxer]

The results you've gotten are suspicious enough that, were it me, I would run a third test using both chronos at the same time.

Then, if there is a difference, you can be certain the cause has something to do with the chronos.

Many folks have run that kind of test and found only a very small difference when conditions did not affect the optical chrono's performance.

 

[Shawnba67]

You said you changed seating depth. I have a 8-06ai and when I seated deeper to get out of the lands. Same charge lost 40fps. This could be some of the loss?? Maybe??

 

[Mikemci]

Now I've been using the CED M2 for many years and haven't had any issues when working up drop charts

^^^^This^^^^

 

[WyleWD]

I've been suspicious for several years now that the sun angle relative to the chrony CED would change its readings. I agree with the other poster that the difference between the two chronographs you're seeing seems like a lot. WD

 

[Ksmirk]

You said you changed seating depth. I have a 8-06ai and when I seated deeper to get out of the lands. Same charge lost 40fps. This could be some of the loss?? Maybe??

Huh? I didn't change anything.

 

[Ksmirk]

Yes this is a magnum and a 215 bullet, SD's with both units are from 8.0 to 14.9 most running 8.0 to 10.3 and I feel the 14.9 is where I ran out of barrel length to burn the case of powder as the velocity dropped off as well so thinking I've found my max just haven't hit the pressure which accuracy is more important to me and I guess the reason the crony readings have me confused.

I'm hoping that this weekend I can run both together and just see what happens but it seems I'm right to trust the CED. Guys I appreciate the replies! it's always nice to know I'm sorta thinking the right way. Thanks and have a great day.

 

[Shawnba67]

Huh? I didn't change anything.

Sorry thought I read that you had loaded long and worked back.
I misread.


Now to save face I'll say you torched enough throat to do the same thing!
I have always wondered how much effect the chrono not being perfectly parralel to bullet path could cause. I never can get mine perfect.

 

[Ksmirk]

Nope, I set the chamber up so I could load long and still get to the lands, get a bit more powder in there so I could gain velocity and keep pressure in check.... done several this way just nothing this big! it's an interesting path for sure when data and past experience isn't lining up like you think it should, plus using Retumbo while all is fine now just waiting to hit that pressure spike that it's so known for.

 

[CharlieNC]

Sunlight factors have a major impact on chrono, as can being a little too close to the muzzle.

 

[Webster]

Yes this is a magnum and a 215 bullet, SD's with both units are from 8.0 to 14.9 most running 8.0 to 10.3 and I feel the 14.9 is where I ran out of barrel length to burn the case of powder as the velocity dropped off as well so thinking I've found my max just haven't hit the pressure which accuracy is more important to me and I guess the reason the crony readings have me confused.

I'm hoping that this weekend I can run both together and just see what happens but it seems I'm right to trust the CED. Guys I appreciate the replies! it's always nice to know I'm sorta thinking the right way. Thanks and have a great day.

CHRONO: If the screens are to close muzzle blast may affect results. Your shooting 2.5 times more powder than I use. Someone was watching me shoot over my chrono a year ago. I had sun screens on. He said the muzzle blast was shaking the hell out of the chrono. I was getting good numbers but didn't realize how violent the chrono was shaking. The sensor, sun screen and supports catch the blast. 6BR 33.5 GR powder. If you use both your chrono's at once and get different results you still won't know which is correct. I would trust the CED? Are your fps with a 210 gr bullet way over the loading manual data. Every manual gives different data. I would be afraid to keep increasing the powder till I got signs of pressure.

 

[Ron Blain]

Chronograph Accuracy Tips – 15 Practical Tips to Increase Accuracy & Reliability is a pretty good read on the subject.

Using or comparing two chronographs is something like the guy with two watches and not knowing what time it is. There is no easy way to know which or if both chronographs are lying or which one is telling the truth. Powder scales become an easy affair with check weights readily available. Unfortunately there is no easy way to check the uncertainty of a chronograph, short of a pile of instrumentation the average hand loader does not have piled on their reloading bench.

With the exception of the new Lab RADAR units most all chronographs work the same. Velocity = Distance / Time where a projectile passes over an optical sensor opening a gate (in a sense) and pulses from a clock (oscillator) begin passing through the gate. The projectile passes over a second sensor which closes the gate. The pulses which passed through the gate are counted. The frequency of the pulses is a known and the reciprocal of the frequency is time. The first room for error is the spacing of the optical sensors, even a small fraction of an inch makes a big difference. Then comes the optical sensors themselves with possible error and finally the internal clock (oscillator) frequency. There is plenty of room for error and considering an average everyday chronograph can be had for under a hundred bucks they are not quite high precision measuring devices. Then toss in other sources of error and it is difficult to get actual honest numbers.

My only concern is how does the fired brass look, how tight was my group and what was the SD (Standard Deviation) of my group. Do I really care if the actual velocity was 2900, 3000 or 3100 FPS? Not really a concern for me. Unfortunately, unlike a scale there is no easy way to check the uncertainty of a chronograph.

Ron

 

[geraldgee]

Temperature difference at the times of shooting?

 

[Ksmirk]

CHRONO: If the screens are to close muzzle blast may affect results. Your shooting 2.5 times more powder than I use. Someone was watching me shoot over my chrono a year ago. I had sun screens on. He said the muzzle blast was shaking the hell out of the chrono. I was getting good numbers but didn't realize how violent the chrono was shaking. The sensor, sun screen and supports catch the blast. 6BR 33.5 GR powder. If you use both your chrono's at once and get different results you still won't know which is correct. I would trust the CED? Are your fps with a 210 gr bullet way over the loading manual data. Every manual gives different data. I would be afraid to keep increasing the powder till I got signs of pressure.

Ya know I thought the same thing! had it happen before with a 243 and some really slow powder, I had one of the fella's at the range watch for me and he stated that there was really nothing going forward but my muzzle break worked wonderfully lol guess he caught a good blast.

As for over book loads you would be very correct! a couple of post prior I stated a 215gr bullet. This isn't the first time I've done this and I'm pretty confident in my loading skills so trust me when I say I go into this project rather leaning on the overly safe side! I've gotten help from some good folks who have been playing with these calibers dang near as long as I have been alive and I have nothing but faith in what they tell me and the data they supply as well as there is no data in the manuals for what I'm doing

 

[Ksmirk]

Fella's this is some good info! I appreciate the advice greatly. I have found out that I can have access to a Lab Radar just have to have our schedules coincide so at least I'll sooner or later have a third data point I'm pretty confident with my CED and this weekend my brother and I are going to take his chronograph out and run some known loads just to see what is going on as he is about to get started on his cannon as well lol at least I have some data that we can do our best to make some good choices as well as the powder he is going to use there is data. Again fella's thank you very much for the advice and direction. Thanks,

 

[C.E.Smith043]

I ran two exact pact models back to back and had 60fps difference between the two units and they are identical units.

 

[mongo chicago]

Be aware that I tested some Winchester Ranger factory loads using one chrono. and there was a variance of 150 fps between rounds from the same box of ammo.

 

[Ksmirk]

These were all weighed charges with SD in the 8-14 range so they were much closer than factory ammo but yes I have seen what you speak of before when a fella at the range wanted to run his hunting loads over the chronograph..... last I spoke with him he had started handloading lol

 

[Texas10]

Here is some interesting reading that might answer some of your questions. Specifically addresses Lab Radar, Magnetospeed and CED M2
https://www.shootingsoftware.com/doppler.htm