Well, it doesn't appear to be the chrono...

Well, it doesn't appear to be the chrono...

This is a discussion on Well, it doesn't appear to be the chrono... within the General Firearm Discussion forums, part of the Related Topics category; I chrono'd three factory loads with MagnetoSpeed and LabRadar. In each graph, the higher line, orange, is the MagnetoSpeed, the lower line, blue, is the ...

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Thread: Well, it doesn't appear to be the chrono...

  1. #1
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    Well, it doesn't appear to be the chrono...

    I chrono'd three factory loads with MagnetoSpeed and LabRadar. In each graph, the higher line, orange, is the MagnetoSpeed, the lower line, blue, is the LabRadar. As you can see, they track almost exactly!





    Although, I didn't list the raw data, it was pretty bad,

    IMI -
    LabRadar: SD = 33.2, ES = 117
    MagnetoSpeed: SD = 30.64, ES = 99

    Outback 69 gr -
    LabRadar: SD = 30.45, ES = 91
    MagnetoSpeed: SD = 29.26, ES = 87

    hornady 75 gr Steel Match
    LabRadar: SD = 29.50, ES = 98
    MagnetoSpeed SD = 26.46, ES = 90

    Notice the high numbers for all three ammos, and the close agreement between the two chronos. That strongly indicates the chrono(s) is not what's producing the high numbers.

    If you look closely at the graphs, you can see the blazing velocity of the IMI 77 gr and the slow Hornady 75 gr Steel Match. Since they both produce high variations at very different velocities, it doesn't look like the velocity is the culprit. Vavg IMI = 2617 fps; Vavg Horn. = 2390 fps. A difference of 228 fps!

    I suppose there should be some consolation in three brands of factory ammo are just as bad as my reloads, it just really means both my reloads and factory loads performed terribly.

    It kinda points to the gun, but i see the same thing across numerous guns, brands, and types (AR & bolt). So the search for an answer continues and the mystery continues.
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    VIP Member Array G26Raven's Avatar
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    The only way youíre going to know which one is correct would be to have another one or two to compare the readings to. Even then you may not get readings close enough to be certain. I donít think thereís enough difference to be statistically significant. But then again, I could be wrong (a rare event 😜)...
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    This would be enough to make me go back to factory loads (if I were reloading and in your position). You have an infinite amount of patience sir!
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    How does that old saying go?

    "A man with two watches never knows the exact time."

    I hope that you eventually solve this variation conundrum.

    It seems to be stumping a lot of members & not just yourself.
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    VIP Member Array HotBrass45's Avatar
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    Do you know where you are on headspace?
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    A little follow up...

    I posted rather quickly last night due to the time and I could have described the purpose better, so I'll do that here.

    With regard to what @QKShooter said about time, "A man with two watches never knows the exact time.", in my field, electrical engineering, we have similar saying, "If you measure the same voltage with two voltmeters, you'll get two different readings."

    So it came as no surprise that I got two different readings from two chronos - and that's ok, but what did surprise me is the difference between the two readings. Actually, I have done this a couple of times before but this time I wanted to see if anything had changed with the MS (MagnetoSpeed) and determine if it was giving occasional sporadic readings which would inflate the velocity spread.

    It appears the MS is NOT sporadic, at least not with the small samples (27 shots) I measured. The percent difference between the LR (LabRadar) and the MS was higher than I've seen in the past. Prior comparisons gave percent differences of 0.5% or less - that's pretty good agreement! This test yielded percent differences of 0.74%, 0.74%, and 0.92% for the three sets of ammo.

    I have to assume the LR is the more accurate, because it is spec'd to 0.1% accuracy and has been compared to very expensive commercial and military Doppler radar units and was found to be VERY close, less than 0.1% (less than a tenth of one percent!) difference.

    I think what is significant here are two things, one there is a velocity offset, i.e. the MS reads higher than the LR. That's OK - that doesn't affect velocity variations due to the MS itself. In fact, when I subtract out the offset the result looks like this,



    And two, the relative accuracy, i.e. from shot to shot, is very good. Where the LR shows a change in velocity, so does the MS and in most cases, as indicated above plot, by the same amount and in the same direction.

    Another interesting thing present in all three ammo sets, is the LR indicated higher velocity spreads than the MS So if anything, , the velocity spreads I've been getting from the MS is lower than it should be

    Here are the numbers from LabRadar and MagnetoSpeed for the IMI set. I chose that set because it had the highest velocity spread.



    Looking at the 4th entry in the table, 2554 & 2595 with a percent difference of 1.6% (that's the worst one), even if the MS is in error by 1.6% as indicated, that would only produce a velocity variation of 41 fps - hardly the 99 fps indicated for the entire set. It is very possible that there was a true 50 fps variation in velocity AND the MS had a 1.6% error on top of that. IF the two were additive, I could see 50 fps + 41 fps = 91 fps. But the fact that I commonly see my buddy's very low numbers - using his MS - kinda refutes that.

    And, there's @OldVet 's numbers that he kindly posted in the other thread - about half of what I got here.

    While I had high hopes the velocity variation problem I continually see would be due to some irregularity in the MS chrono, that doesn't appear to be the case.

    So, the search for an explanation and fix goes on???
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  8. #7
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    Quote Originally Posted by HotBrass45 View Post
    Do you know where you are on headspace?
    Thank you for the thought! I obviously need all the thoughts I can get!

    I set and measure headspace to 0.003" under a fired case dimension. I size and measure about 10 cases until I'm confident the sizing is consistent and then I just size away.
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    Quote Originally Posted by G26Raven View Post
    The only way youíre going to know which one is correct would be to have another one or two to compare the readings to. Even then you may not get readings close enough to be certain. I donít think thereís enough difference to be statistically significant. But then again, I could be wrong (a rare event 😜)...
    True, but it's not so much about which one is "right", but do they essentially track with each other.

    "We" were suspicious the MS (MagnetoSpeed) may be giving disproportionate or incorrect sporadic readings, which would inflate the variation, but comparing the MS to the LabRadar indicates that's not the case. There is a small velocity offset, 41 fps for the worst case.
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  10. #9
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    Quote Originally Posted by G26Raven View Post
    The only way youíre going to know which one is correct would be to have another one or two to compare the readings to.
    Tangle on his next chrony test...
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    I don't know if absolute accuracy is important with the chrony as much as consistency is. Both seem "consistent," and does +/_ 40-50 fps reading between chroneys change anything?

    Tangle, for a nominal fee I will reload ammo for you. I promise to load powder in them too!

    FYI, I set the headspace to -.004-.005 on my Mongoose cases. .003 and I can feel the bolt bind a bit when opening. I may lower that to .003-.004 later, but I really don't need to add any experimental cycling issues at this point.
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  11. #10
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    Quote Originally Posted by OldVet View Post
    ...
    I don't know if absolute accuracy is important with the chrony as much as consistency is. Both seem "consistent," and does +/_ 40-50 fps reading between chroneys change anything?
    You're right - well, long distance shooting excluded. And since I'm not really doing long distance shooting, the absolute accuracy is as you observed is unimportant.

    Where absolute accuracy is important is for ranges longer than I have access to - 1000+ yards. Then, small errors in velocity can produce complete misses, but all that's irrelevant for me.

    So you're exactly right, consistency is more important than absolute accuracy.

    This little test was just to see if the MS was giving aberrant measurements, but as you noted, "Both seem consistent..." so I don't think the inconsistencies I'm getting are due to the chrono. After all, you, and others, are using the same set up and getting much better consistency.

    Quote Originally Posted by OldVet View Post
    ...Tangle, for a nominal fee I will reload ammo for you. I promise to load powder in them too!
    LOL - you better be careful what you're volunteering for! At this point...

    Quote Originally Posted by OldVet View Post
    ...FYI, I set the headspace to -.004-.005 on my Mongoose cases. .003 and I can feel the bolt bind a bit when opening. I may lower that to .003-.004 later, but I really don't need to add any experimental cycling issues at this point.
    Sounds wise to me!
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  12. #11
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  13. #12
    VIP Member Array OldVet's Avatar
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    I think you angered the powder gods.
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  14. #13
    Distinguished Member Array patkelly4370's Avatar
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    I have only skimmed the pertinent threads.
    My question, are these all through the same firearm? Have you checked these reloads through a different firearm?
    You seem to be covering bases well.

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  15. #14
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    Quote Originally Posted by patkelly4370 View Post
    I have only skimmed the pertinent threads.
    My question, are these all through the same firearm? Have you checked these reloads through a different firearm?
    You seem to be covering bases well.

    Sent from my SM-G955U using Tapatalk
    Thanks for the post. Yeah, oddly, strangely, eerily, mysteriously, it seems to be true across guns, ARs and bolts alike. In fact, in one of my latest chrono outings, my semi had better numbers than my bolt gun - who is that possible!
    We don't have a gun problem in the US, We have a people problem.
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    in Gun Free Zones.

  16. #15
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    Quote Originally Posted by OldVet View Post
    I think you angered the powder gods.
    Man, I reckon so!

    I'm about ready to believe something like that. Anybody know anything about a reloading curse - and how you get out of it!
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