The guy shooting next to me let me use his Garmin one. Only the size of a fat cell phone, sitting on a little tripod on the bench alongside the rifle. Not having seen one like this before, that just blew me away ... as does the $400-700 price tag. Anyway:

20-inch Howa 1500, caliber 7.62x39, Norma Range & Training 124 FMJ:
Shots: 5
Minimum: 2376.0 fps
Average: 2412.1
Maximum: 2448.4
Extreme spread: 72.4
Standard deviation (whatever that is): 25.1

Jibes closely with the advertised 2430 fps.

22-inch Browning AB3, caliber 6.5 Creedmoor, Norma Golden Target Match 130 open tip (doesn't say if boattail or not):
Shots: 5
Minimum: 2809.3
Average: 2816.4
Maximum: 2828.9
Extreme spread: 19.7 (very consistent)
Standard deviation: 6.9

2,816 f/s works out to 858 m/s, slightly below the advertised 869 m/s, but they probably took theirs from a longer barrel than my 22-inch.

The range I've been using is in western Greene County, TN, and is run by the county. It has a few shortcomings but is by far the friendliest range I've ever used. The shooting areas are only monitored remotely by TV; everybody is more or less on an honor system. I have yet to see anyone break it. The ROs know and greet me by name. And the guy I mentioned in the first paragraph is just one of many such encounters. He told me that he was shooting a 6 GT-caliber with a muzzle brake and it would be loud. I said, "Don't worry, unless you're going to shoot at me, nothing will bother me." Another time I was sighting in a 5.7x28-caliber carbine with a non-magnifying sight but forgot both my binoculars and spotting scope, so I couldn't see my bullet holes even at the 25-yard line without walking at least halfway up. The guy next to me took time out to spot using the high magnification setting on his rifle scope. If I go on a weekday (Wed. thru Fri.), from about 3 PM-6 PM closing time I practically have the place to myself.

I have had my Garmin since they first came out. Yes the price was/is steep, but I use mine almost weekly.
Have let others use mine (while I was at range) and a couple of them have since purchased their own (some bought the Althon brand).

PC

Mine is used on EVERY trip to the range or desert.
They just don’t make an easier one to use…except maybe Athlon. I have not had any exposure to that one.

quote:

Originally posted by egregore:
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22-inch Browning AB3, caliber 6.5 Creedmoor, Norma Golden Target Match 130 open tip (doesn't say if boattail or not):
Shots: 5
Minimum: 2809.3
Average: 2816.4
Maximum: 2828.9
Extreme spread: 19.7 (very consistent)
Standard deviation: 6.9

2,816 f/s works out to 858 m/s, slightly below the advertised 869 m/s, but they probably took theirs from a longer barrel than my 22-inch.

Single digit SDs from factory ammo is excellent.

I prefer using 10 shots minimum worth of data but 5 is better than nothing.

I use mine while practicing so I usually have fairly large sample sets that I use for my AVG FPS.

It usually doesn't change significantly after 10 shots.

I have owned chronographs since Oehler was the type to have (and I still have two), and I frequently use the Garmin that is with me every time I go to the range. They’re hardly necessary if our range sessions consist of mag dumps and/or nothing but Bill Drills, but they are useful for evaluating manufacturers’ velocity claims, developing handloads, and especially for long range precision shooting.

Units like the Garmin Xero (and the Chinese knock-offs) are easiest to use these days. Before the Garmin I used the LabRadar which employed the same Doppler radar, but it was not quite as convenient, partially due to its size, but mainly because it requires a trigger of some sort to start tracking the bullet. I found that process to be somewhat fiddly as compared with the Garmin. The biggest advantage of the LabRadar is that it will provide downrange velocities as well as MV, but I suspect that’s not a feature most users use(d). I believe the Garmin and the knockoffs have killed the LabRadar which can probably be had very inexpensively when found.

Another disadvantage of the radar units is that they require a certain amount of bullet flight distance to read the velocity. They don’t work if we want to know the impact velocity of a bullet into a block of gelatin at 10 feet. For that purpose the way to go is with a unit that uses Sky Screens (®?). Those devices, though, are generally considered to be less accurate, especially the common ones with very short screen separation. I used the Oehler units with 4 foot separation, and as I recall the separation could be set as much as 12 feet for greater accuracy.

To use chronograph data properly does require some understanding of statistics. For example, anything less than a sample size of 30 (e.g., 30 shots measured) is considered to be a “small” sample, and a sample size of five is about useless except for very general information.

The problem with small sample sizes is that chance plays a bigger part in the data.

For example, I have a velocity series of IMI 77 grain OTM, LR, Mod 1, consisting of 14 shots fired from a Wilson Combat rifle. That’s a very small sample, but what if I fired only five shots and got these figures which were part of the actual 14 shot string: 2728, 2728, 2731, 2724, 2727. The extreme spread would be only 7 fps, and the standard deviation would be 2.2, both of which are extremely small for a string of velocity figures, and which by themselves would give the impression that the ammunition was extremely consistent.

On the other hand, what if my five velocities (also from the actual string) were 2704, 2720, 2751, 2775, 2806 fps. The extreme spread is 102 fps and the standard deviation is 36.8—both of which are horrendous. The actual standard deviation for the 14 shots was 25.4; still bad, but better than the cherry-picked 36.8 fps result.

Standard deviation (SD) is a measure of how closely the elements of the data set are the same. For example how close to the average are all the velocities that were measured. Precision rifle shooters like to see SDs as small as possible, but ideally less than 10-12 feet per second with a good sample size. Extreme spread is another useful figure, but only if it’s understood correctly. If the ES is 150 fps, and yet the SD is only 12.5 fps, that indicates that there was probably a measurement error or other problem with a single velocity figure.

Large sample sizes are more likely to produce greater extreme spreads than small samples; the standard deviations may be better—or worse—but almost always will be more accurate and useful.

(I am not a professional statistician, so anyone who is, please jump in with any corrections or clarifications.)

quote:

Originally posted by KMitch200:
Mine is used on EVERY trip to the range or desert.

I paid full boat for mine when they came out and I don't regret it one bit. It gets used pretty much every trip to the range with a rifle. I owed 3 traditional chronographs prior to that. The Garmin probably saw more use in the first year than the other 3 did in total in the last 40. So simple, so hassle free. No wires, sky screens, no full sized tripod, no fighting the sun, no fighting the wind. When I set the Garmin on the bench, I think about the countless range hours wasted setting up and breaking down the old one, even as infrequently as I used it.

MEASURING Velocity is just a whole different thing from reading estimates from a manual. People should stop and think for a bit about that.

The new radar chronographs are such a HUGE step forward from the old sky screen etc that new shooters just don't know how good it can be.....

Newer shooters PLEASE listen closely to this: Use your accurate ballistic Data from your Chronograph to determine your BALLISTICS and NOT your Load Data!!!!

If you are getting higher velocities than the pressure tested manuals you are 99.9% likely to be using higher pressures.

Stay within Pressure Tested Manuals limit and use the ballistic data from those.

Why risk blowing up a rifle for a couple hundred fps? Just buy a hotter caliber...............

Accurate chrono data is very important part of rifle shooting -- safety and flight ballistics are at the top of the reasons. The older chronos were a pain to set up. MagnetoSpeed was a massive step forward; Garmin even more so.

I use chronos with new barrels, new loads, and old barrels.
- New barrels need MV data, as every barrel is different. Some differ by a lot, others by a little. Barrels almost always speed up over the course of their first 100-ish rounds, therefore testing is rarely "one and done" on the first outing.
- Load testing is important for all ammo, both factory and handloads.
- Shoot enough, and a person will wear out a barrel. Decreasing MV, increasing dispersion, and frequent low fliers are all indications of a shot-out barrel.

I don't use a chrono all that often -- meaning it sees some of the first 100-200 rounds and the last 100-200 rounds of a barrel's life. Now if I had a Garmin instead of a MagnetoSpeed, I'd probably clock MVs more frequently. But I rarely shoot from stationary positions for more than a few rounds -- it's shoot and move. I try to practice more from alternative positions and barriers than from stable positions. I honestly don't know how many years it's been since I shot from a benchrest.

I probably view MV numbers differently than many shooters. I don't test MVs over large strings, unless there are issues with a load. I'll shoot a couple of 5 round strings at various times of one day, then the same routine on another day. If they're relatively consistent, then I'm done -- until down-range results indicate different flight ballistics, in relative terms for the caliber and distance to target. MV variations for 308 Win don't mean much for someone who shoots targets of 300 yards or less. MV variations mean a lot for someone who pushes their 308 Win to 800+ yards.