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Old 01-24-2013, 12:43   #16
TDC20
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Thanks for all the responses, guys. Some interesting things here to consider.

Quote:
Originally Posted by Taterhead View Post
One thing to consider if velocities were way out of line. No powder has given my chronograph fits like Blue Dot. I have to get WAY back or I get readings that don't "track." They are usually higher than expected with high spreads on velocity. Also, my chronograph wants a pretty full battery too.

I would be inclined to consider potential chronograph errors first before concluding that Blue Dot is that severely reverse temperature sensitive. 40F is not really that cold.

Any rate, just a thought.
Well, I have serious misgivings about trusting my Shooting Chrony. I have noticed several problems over the years, mainly a lot of missed shots when the battery starts to wear down. This is a big flaw, IMO, of the Shooting Chrony brand. If you have ever wondered how the voltage in a battery decreases as it wears down, look at the last page of this datasheet http://data.energizer.com/PDFs/522.pdf A 9V battery isn't actually 9V for most of it's serviceable life. So I fixed that by adding a DC-DC SEPIC converter between my 9V battery and my Shooting Chrony that guarantees a constant regulated 9V at the Shooting Chrony 9V input, even when the battery is only putting out 5V, and that has fixed much of the problem with lost shots.

The other issue is the optical sensors. I think that certain angles of sunlight hitting them sometimes can fool the sensor and miss a shot. And then finally, I honestly believe there is some kind of firmware bug in the microprocessor code that causes me to get 3000+fps velocities when I'm shooting 1100fps loads, and vice versa, once in a while. It keeps doing it unless I power off and power back on. That is really irritating. However, when it's working, in spite of the problems, I usually trust it. An occasional wild velocity is considered a bad reading, and I move on. But when I'm getting low standard deviations in 5 or 10 shot strings, I'm believing the data.

That being said, on this day, the old lot of BD 5 shot string ran an ES of 17 and a SD of 8.35. Same load with the new batch of BD ran ES of 39 and SD of 14.61. Plus, since I already had the Chrony up and running, I fired off a 10 shot string of my 175 LSWC Bullseye loads. That 10 shot string ran an ES of 40 and a SD of 11.61, and it clocked only 19fps faster than the same recipe (could have been different brass, I don't know) that I chronied 18 months ago. But the 175 LSWC's averaged 288fps slower than the BD 150's. So, looking at all of this data, I tend to believe that the numbers are correct. The Bullseye load tends to be smokey due to the cast bullet lube and Bullseye in general, but I didn't lose any shots or have any wild velocities in that 10 shot string. It was shot the same distance (8-10ft) from the Chrony as the BD loads were.
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