Chrono accuracy

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by bkondeff, Aug 9, 2011.

  1. bkondeff

    bkondeff Well-Known Member

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    So I have been using a Chrony Beta Master for a few years. Over the past 2 years I have noticed unreasonble differences from one outing to the next in my 7mm between 2880 and 3020 fps. I have attributed some of it to the level of the sun, with overcast days the best. I decided to pick up a new one and basically test them against each other. I placed one directly in front of the other. I came up with ~100fps diff. I thought maybe the one in front affected the one behind it, so I swapped their position and it remained the same. I made sure both units where properly unfolded.

    Any opinions on the diff or how to verify/fix it? I will say on this day the vel of the newer unit seemed less realistic at 3050 fps in my 7mmRM for 71.0 gr Ret on a 24" sako. I have had this speed before when my bullets where Jammed in, instead of kissed.
     
  2. Trickymissfit

    Trickymissfit Well-Known Member

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    everytime I see somebody using a Chrony at the range they are constantly fiddeling with it. Is it their setup? I don't know. I use a Pact PC2, and have zero complaints about it, except the lack of a printer.

    You might try moving the light screens out to about fifteen feet from the barrel to see if the blast from the barrel is causing some of the problems. I seen some folks have to move out to twenty feet with .300 Weatherbys.
    gary
     

  3. J E Custom

    J E Custom Well-Known Member

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    I use the Oehler 35 P and find it to be very accurate (And consistant) when checked against
    other chronographs.

    Sometimes all chronographs will act up if the setup is not good or the light is bad.

    One of the members has a set up that has 3 different chronographs on the same bar,
    maybe he will chime in.

    Any chronograph may be off a little from one to another (10 to 15 ft/sec) but no more.

    Loads can vary depending on weather conditions and type of powder but they should be
    consistant in like conditions.

    My screens are set 4' apart and I set them 16' from the muzzle so I can get true muzzle
    velocity by measuring velocity drop between screens and x4 . I know it is not perfict but
    it is very close. Plus it gets the screens far enough away to keep the nuzzle blast from
    skewing the velocities.

    J E CUSTOM
     
  4. Broz

    Broz Well-Known Member

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    I have owned a "shooting Chrony" for many years. First one was a gift from my wife in 1998. After sometime I got a "deal" on a second one to compare. I set them up inline on a 2x6 and they both read inline. No matter which is first one of the units i always 25 to 40 fps faster. So, I bought a Pact with IR screens... It never read a single bullet. My shooting chronys hardley ever miss a bullet. :rolleyes: I sent the pact back. I recently purchased an Oehler 35 with proof screen. I feel I now own a good accurate chronograph, if there is such a thing. Someday when I have time I plan to see which shooting chrony is closest to the Oehler just for grins.

    Figure your drops from 500 , 700 and 1000 and see what velocity your program needs using an advertised BC for your bullet. This might tell you which one or if both are lying.

    Jeff
     
  5. Trickymissfit

    Trickymissfit Well-Known Member

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    Never saw one with the inferred screens, so can't comment on them. I use the plain jane generic ones that it came with, and over a few years (about 12 to 15 to be exact) I doubt it's missed eight shots, and probably closer to six. For about ten years I shot with a buddy that used an Ohler 35, and we could see zero difference between them except $200. If his threw a round out, mine did as well. The difference in velocity usually was about six to eight feet per second. Who was right? Nobody will know. We later built a completely new bracket to hold the screens as the Ohler outfit was nothing but a tomato stake on a good day, and his spreads did tighten up a slight bit.

    Calculating the actual velocity of a bullet should be easy if the bullet manufacturs told the truth about their actual B/C's. Most simply guess at it.. Plus you add in the error of the shooting position, and it's guess work
    gary
     
  6. Broz

    Broz Well-Known Member

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    I usually get it worked out pretty close to the advertised BC's, with Bergers anyway. But in the end as long as my cold bore shots are right on within the capability of me, my rifle and ammo, I really dont care what velocity or BC numbers are used. They are just numbers. The proof is in the pudding.

    Jeff
     
  7. J E Custom

    J E Custom Well-Known Member

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    The main thing i like about the Oehler 36 P is the proof screen and the printer.

    The proof screen gives you two velocities and if they are different by a small amount it gives
    you an error message so you know something went wrong with the chronograph and not with
    the load and you can delete it from the other shots, And you don't have to guess if it is working.

    I also like the printer because it gives you much more than the velocity and while at the range
    testing loads I simply write the load number on the printout and I can look all of the test over
    for a better comparison.

    It is also a permanent record in my loading book.

    The Oehler 35 P is expensive but I think It is worth it considering how much data it gives you
    that is invaluable and the money it can save you if used right.

    J E CUSTOM
     
  8. Broz

    Broz Well-Known Member

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    bkondeff, One thing I did learn about the Shooting Chrony's is they are sensitive to muzzle brakes. As are most Chronographs. Get thatthing out there at least 18 feet.

    Jeff
     
  9. Trickymissfit

    Trickymissfit Well-Known Member

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    the guy that I shot with, that owned a 35 said more than once that he felt the proof channel was a sales gimmick. I had no opinion concerning that, but he did. Nobody ever said the Ohler wasn't a great chrnograph, cause it is. Just $200 over priced before you buy the Square Peg mount at $300+. In the end some folks will buy a Lexus, and some folks will buy a Chevy, and both will get to the same place just the same.
    gary
     
  10. Boss Hoss

    Boss Hoss Well-Known Member

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    Edited
     
    Last edited: Nov 9, 2011
  11. Trickymissfit

    Trickymissfit Well-Known Member

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    Nobody has ever said that an Ohler 35 is junk, cause that would not be true. But the guys with deep pockets love to run down the other guy's stuff down with little if anything to build a case on. Doug did improve upon the Ohler setup with a custom mount that I built for him. It tightened up the extreme spead a little bit using loads he knew were dead on. I've shot thru Doug's in just about every form of shooting condition except snow & ice. I've also shot thru mine thru about every condition without a hitch. Is his more accurate? Can't prove it by me, or anyone else that's shot thru it. Is mine better or just as good? Once again I see no real difference between the two. Is there room for improvement in the two of them? Yep! Pact and RCBS developed a software package for the PC2 when it first came out, and they never marketed it as they couldn't find a calling for it amonst the shooters. Now I think it would sell like hot cakes. Basicly it connects the Chronograph strait into a notebook PC, or allows you to down load all data into your home desk top. Of course they could do the samething with an SD card. The one thing everybody seems toforget about is there is no real way to calibrate a chronograph There is no proof load you can buy that will be exactly the same every shot. Be nice if there was, but it ain't happening anytime too soon. So you take your data as it's presented, and live with it. You can't prove it's right, but you also can't dissprove it either. I see absolutely no reason to get up in the air over six feet per second at 3500fps!
    gary
     
  12. bkondeff

    bkondeff Well-Known Member

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    Thanks for the feedback. I have learned or confirmed a few things.

    At this point I feel I have mitigated concerns regarding the difference being related to light issues, not enough distance from muzzle, etc. as with having both set up back to back and then switching them with no reversing of the difference between the two it tells me the difference is in the units themselves. The problem is, which unit is right, or at least "most" right. 100fps is significant. I think the one round I have that is the most consistently "known" velocity is my 17HMR in my savage. I have chrono'd the loads before and they were damn consistent to the 2550fps listed on the box. I will do the same this weekend and shoot the 17 and see which Chrono is the closest. I will also diligently measure the dist between the screens. I am averaging about a 3.4% difference in measured velocity so I assume the math should be simple if one set is 3.4% closer than the other(~.4") I may know my answer.
     
  13. Greyfox

    Greyfox Well-Known Member

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    With the desire to have very accurate velocity info I broke down and bought a 35p. After two of the lower priced chronographs consuming a lot of time and living with uncertainty and inconsistency , I should have bought one in the first place. It was a false economy.
     
  14. Trickymissfit

    Trickymissfit Well-Known Member

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    Not picking a side or anything with the 17HMR, but I would tell you this. The only way to accurately base a testing number is to use three identical pieces of equipment (or more) to build a base number off of (that's the way labs test stuff). Assuming the 2550fps is an accurate figure, I would use it as a base figure. Then I would simply try several under the exact same conditions (sameday and about the same time of day). Try to shoot everything out of the barrel with a temp fairly close. In otherwords a cold barrel or a warm barrel. I would expect to see as much as a 12fps difference between each unit you test out, cause they are different. And who knows which is actually dead on the money. If I were testing chronographs, I would use something like a 6PPC or a .222 Remington. Use one single case and a lot of bullets that were all weighed prior to loading. Try to make each load as exactly the same as possible. The otherway to do this is to actually measure the case volume in grains of water they hold, but then you have to deal with slight external differences in the neck and shoulders.
    good luck
    gary