Recent content by gregmark24

I, for one, think Hornady has a good argument. I have a 243 that seems to prefer a given powder charge and not prefer another. I’m going to load up 20 of each and put Hornady’s results to the test. Chronograph and POI both

Here’s the Hornady graph at 0.2 GN increments. Dismiss the holes between those peaks.

In reality, and in my case, it should allow a direct comparison between similar velocities measured on my LabRadar, and my buddy’s new Garmin. But, though average and ES compare well, SD does not, with the Garmin often besting the LabRadar by an SD of 2. So, if you’ve got an ES and SD goal for...

I beg to differ. Garmin calculates it WRONG. First, we're assuming a normal (bell-shaped) distribution. Not a bimodal, triangular, square top distribution, etc. Most of us are shooting smaller samples of data, well under 30, and more likely 5 to 10 shots looking for an average velocity, ES...

Yep. You're spot on. By using a "sample", you're admitting that you don't have all the data from a normal population, and your SD should be worse. Some almost 50 years now since my statistics class in college, I still have occasional dreams that I'm going to my statistics final exam, but...

I didn't find IHFarmer's post, but in another thread, we've discussed this Garmin SD issue extensively. Garmin calculates (an optimistic) SD for small sample sizes. Less than 20. For 3 shots, the SD from Garmin will always be too optimistic. For 50 shots, it will be correct. As an example...

Yep. As I had brought up early in this thread, your results are very similar to ours. LabRadar and Excel calculate SD for small groups as a small sample size, but Garmin calculates incorrectly, for a large population size. My second polite notification to Garmin a month ago regarding this...

I think it does make a difference. If you're shooting 3 rounds per powder development charge, the difference in reported SD is huge with the correct vs Garmin (optimistic) results. If you use a spreadsheet after the fact, or a LabRadar, you'll get correct (less optimistic..) SD's.

I contacted Garmin about the STDEV.P vs STDEV.S what, two weeks ago? I've never gotten a response; that's really disappointing.

I’ve contacted Garmin about their SD miscalculation and will report back on this forum if I get a reply from them

I think for anything past 30 or 40, STDEVP is fine and even STDEV will bring you plenty close. However for the small ladder rounds of 3 to 10, you need to use STDEV, or you’re lying to yourself that you truly have a normal population with a small sample size.

Yes! Also my favorite. I have both the 12 and 20 ga in a 28" modified. Both old, and I typically use the 20 ga. Love them....

It is possible that Garmin truncates the extra digits to the right of that 0.1 place instead of rounding. Regarding your large sample vs population Excel differences, sample (STDEV) will always produce a larger result than population (STDEVP) because the denominator will be N-1 for sample and N...

Ok. We're there! My buddy mis-typed his Garmin-read SD on the 2nd string of three shots. He typed 9.3, and it should have been 9.8. Standard Deviation for his sample (small size) should have been 12.0, but the SD for a population (large sample size) is 9.8. Garmin calculated for the wrong...

The Garmin is calculating SD way too low, ie optimistic. 9.3 vs 12.0. I believe the actual displayed velocities are accurate, and don’t know if my friend’s early-made Garmin is calculating SD wrong from three velocities, or if all Garmin’s are. I’m hoping other folks with both Garmin chrons...