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Chrono accuracy

 
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  #1  
Old 08-09-2011, 10:19 PM
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Location: Star, ID
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Chrono accuracy

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.
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  #2  
Old 08-10-2011, 10:17 AM
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Re: Chrono accuracy

Quote:
Originally Posted by bkondeff View Post
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.
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
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Old 08-10-2011, 11:34 AM
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Join Date: Jul 2004
Location: Texas
Posts: 5,509
Re: Chrono accuracy

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
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Old 08-10-2011, 12:15 PM
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Join Date: Feb 2007
Location: Townsend, Montana.
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Re: Chrono accuracy

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. 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
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Old 08-10-2011, 03:01 PM
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Re: Chrono accuracy

Quote:
Originally Posted by Broz View Post
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. 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
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
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  #6  
Old 08-10-2011, 03:49 PM
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Location: Townsend, Montana.
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Re: Chrono accuracy

Quote:
Originally Posted by Trickymissfit View Post
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
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
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  #7  
Old 08-10-2011, 07:17 PM
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Join Date: Jul 2004
Location: Texas
Posts: 5,509
Re: Chrono accuracy

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
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