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Chrony readings vs published data

 
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Old 05-08-2009, 06:12 PM
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Chrony readings vs published data

I am getting readings on my chrony that are 100 fps lower than published data. Sometimes more. Using same bullet, powder,primer and barrel length(257 WB). I contacted Chrony and they insisted that the unit does not need to be calibrated except every 10 years if that. Does anyone know of a test method for a chronograph? When this first happened the shells had been sitting in the cold and it was not extreme powder. Hogdon said you can get anywhere from a 200-400 fps variation from 0-125 degrees F With some of there powders. I was around 250fps low. It was around "0" ,and the shells had been sitting in the cold, so I chalked that up to the temp. I shot some more of the same load in the spring and it was better but only by 1/2. I also have a 280 Rem and that has been right at 100 fps off on the publised data. Nosler did say that the test barrels they use produce higher velocities. Do match grade barrels produce hight velocities? I have been kicking around the idea of getting another chrony and mounting them inline to check each other. Any one do this or do you just trust the chony?
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Old 05-08-2009, 06:27 PM
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Re: Chrony readings vs published data

Your chrony is most likey very accurate.

Yes, some of the match grade barrels out there can and will produce higher velocities at a given powder charge weight. This is due to tighter tolerences and smoother finishes. Less powder is usually required to get top velocities.

When you have an understanding of bore qualities and tolerences, chamber tolerences, powder lot variations, free bore variations, you can imagine that 100 FPS really isnt that suprising.

The bottom line is that IF YOU ARE ABSOLUTLY SURE that you are not having pressure issues at the charge weights you are at, add more powder. If you are 100 FPS under book max and pressure signs are not there, then you can usually add more powder to get the velocity up. But to answer your questions, 100 FPS lower than published is normal. So is 100 FPS higher. That said, it is ALWAYS a good idea to start low and work up instead of the other way as 100 FPS higher than published in some calibers is VERY dangerous.

Hope that helps.
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Old 05-08-2009, 06:39 PM
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Re: Chrony readings vs published data

That is really what I was looking for. Chrony told me the only way to check if my unit was good was to go by the published load data. Well, if it's off one would think the unit is bad if all other variables are there. No, pressure signs at all. I am waiting for a new stock for the 257 and then I will resume shooting that again. Right now I have been focuse on the unltra light WB in 280 and finding a load to shoot in that. 140 accubonds have been shooting great but as soon as I start loading it up to max or slightly above max to make up the difference in fps it starts to spray. I am assuming due to the thin barrel but so far 3/4 and under. But 3/4 is the norm. Will light barrels stray when pushed?
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Old 05-08-2009, 08:46 PM
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Re: Chrony readings vs published data

I am one that believes that if youre running max or over max, it is time to back off. If youre running into low velocity/high pressure loads, then you may concider trying a different powder.

Use the right powder for the job. Sometimes due to various circumstances, realoding manuals can only be used as a rough guide. Sometimes you may need slower or faster powders than recomended. An example would be if youre using a tight bore and very tight cut chamber with minimal free bore, you may need a slower powder than what is the norm.
__________________
Long range shooting is a process that ends with a result. Once you start to focus on the result (where the shot goes, how big the group is, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
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