Odd Chrony #s...

[44Blam]

I went to finish my chrony work on 44 magnum with AA #11FS and I got some odd results.

Initially, I started testing and then I accidentally hit the back screen. :shock:

Anyway, I got a new back screen and took some loads out to finish my testing.

Gun is Ruger Redhawk with the 7.5" barrel, boolit is Accurate 43-240AG - gas checked and powder coated. WLP primers. AA Test data is:
ACCURATE NO. 11 FS (continued)
240 SIERRA JHC 19.2 1,321 22.6 1,554 35,728 1.590

My initial, testing was:
19.5 grn 1411, 1408, 1411, 1410, 1416
20.0 grn 1412, 1421, 1424, 1425, 1432
20.5 grn 1439, 1443, 1439, 1445, 1447
21.0 grn 1451 (POW) dead chrony.

My testing the other day was:
21.0 grn 1229, 1199, 1250, 1292, 1162
21.5 grn 1246, 1290, 1302, 1258, 1291
22.0 grn 1314, 1387, 1278, 1343, 1329
22.5 grn 1334, 1341, 1390, 1399, 1359
22.8 grn 1383, 1380, 1412, 1433, err

I was a little confused at the #'s so I sent 6 rounds of my unique load (8.5 grn) through that tends to be about 1100 fps and got:
8.5 grn 640, 578, 1170, 1165, 1183, 1041

Now, the loads at 21 grain FELT like a full house round. Just like a W296 load... But 1451 to 1200 or so is a big drop and I was very careful making these guys since I only made 25 and I was going to test them...

The first day was nice around 70 degrees and the next day was closer to 85 degrees. Also, I had the chrono a little closer maybe 5-7 yards instead of 10-15 yards - this was to decrease the chances of clipping the back screen again...

But then the Unique #s also made me think that the #s weren't right... I had been shooting that all day in a steel match and there was no variance in shooting or felt recoil...

My chrono is a Caldwell G2.

But what could cause these odd differences in #s???

[David2011]

This may not be a bit of help but it’s all I have to offer. The only time I’ve had odd readings as when I set the chronograph up too close to the firing line. It was seeing bits of powder and giving very low readings. From that day forward I’ve used a tape measure to make sure that didn’t happen again. Problem is, I set up ten feet from the muzzle and you’re already beyond that so you may not be measuring the velocity of powder.

Another thing I do is set up on a target down range. That provides a consistent aiming point so I don’t shoot the chronograph or screens.

[upnorthwis]

Could be temperature related too. While I have not used Accurate #11, I've noticed wide variations with WW231, 5744, and H4895 when shooting with temp differences.

[mattw]

May well be that you were to close with a magnum, the darn things will catch the blast cloud and get all confused. When I chrono magnums I tend to set the unit 8 to 10 feet away. I have also noticed on my that if we have a storm moving in with lots of cloud movement and color contrast the unit will sometimes log an err or will come up with a really odd speed, either very slow or very fast.

[Shuz]

I have found that different light conditions can cause erratic readings with my Oehler 33 sky screens. Best days to chrono I've found are cloudy days with no sun. That way, the same amount of light hits each screen. Real erratic readings can be obtained when 1 screen is in the sun and 1 in the shade.

[JBinMN]

I have a Caldwell and when I first got it I took a BB gun & ran 10 BBs thru the chrony & got a "benchmark" for speed using the BB gun. I then took a .22 Ruger pistol & using the .22 got a "benchmark" on those rounds from that lot of .22LR.

That way I have that set of "benchmarks" to use when I test to make sure the chrony is giving me accurate numbers. So, when I test any other calibers I can run some rounds of BBs or .22LR beforehand to make sure that the velocities are within the range for the conditions. Any changes up or down in velocities from those "benchmarks" should be reflected in what I get for readings in the calibers I am testing.

I mention this all because you said you used a Unique load to check your chrony & see if it was being accurate. The resulting numbers you gave were within what you said was the approximate "benchmark" velocity for that Unique load ( You did not mention if you used the same firearm each time for the benchmark approx. of 1100FPS but I am thinking you would for accuracy sake) with the exception of the first 2 shots fired & then the error at the end.

So, since you have a "benchmark" using that Unique load and it seems that the chrony is reading somewhat in the velocity of 1100FPS with an occasional "stray" from what is that 1100FPS when you use it, I would suggest you take the time to test your benchmark Unique load as often as you can for a week or so , at whatever environment/weather conditions you are dealing with each time & record the velocities you get for those conditions using that "benchmark" load. I would also suggest you do the same with a .22 or similar , relatively inexpensive round( even another caliber/powder you load, if you like) that you can get in bulk( several hundred to 1000) to maintain the "lot" for another benchmark load to fall back on.

Using the same "lot" will help establish that you are not getting too much variance in your "pre-tests" using the benchmark loads, and then you can compare those recorded benchmarks to the testing of the calibers you subsequently test.

Basically what I am saying is that if you chose to use the Unique load for the benchmark& record that it is slower in velocity on Sunny days and faster on Cloudy days, then you could expect that the results of any testing you do on the corresponding Sunny or Cloudy days would be slower or faster as well. The same for if you use another "benchmark". { If you have read any of Mr. Larry Gibsons test results using his chrony & pressure testing equip., you will see that he maintains a "lot" of "benchmark" ammo to use to verify his equip is operating within its "usual"/normal parameters before he tests the rounds he wishes to test. I am just doing the same thing with my chrony & am suggesting you do the same to establish those "benchmarks" to use to compare when you test.}

As far as your question,
"But what could cause these odd differences in #s??? "

Here are some possibilities:

Changes in Sunlight or shade.

Changes in distance to chrony from muzzle

Changes in barometric pressure, temperature, & other environmental/weather conditions.

Faulty Chrony

Or a combination of all the above. There may be some more things, but that is all I can think of at this time.

You are going to have to set yourself up with some sort of "benchmark(s)" that you record & "know" when the chrony is doing what it is supposed to be doing "before" you test the things you wish to test to keep from having things like is being questioned now,, and as well, to verify that your chrony was not damaged inside in some way by the shot that hit the back screen. That is why I mention doing some testing of the chrony with an established lot of ammo for a while to see if it is doing it with that "lot". If it continues, then perhaps your chrony needs some repairs, and at least if it is not damaged, you will be more confident it is OK & still have the recorded benchmark data for the future if such things happen again.

I was going to post this the day you first asked, but hesitated as I thought you would get more replies & save myself the typing.

So, you now you have "my opinion" on what "I" would be doing to investigate these readings & you can choose to do the same, or pick a different path to take to find out what is going on with the chrony.

G'Luck! in whatever ya decide to do!
:)

P.S. - You must make sure to place the chrony at the same distance each time & make sure ALL things you can control are the same each time you test to get a correct & established "benchmark". Even if you change one thing, such as adding "shades" to the chrony when you have not used them before, or moving from 15ft distance to 20 feet distance from the muzzle of the firearm, can have an effect on the results. The environment/weather conditions can change, but the "set up" should remain the same. If you are wanting the option to add sun shades to the chrony, or change other things in the setup, then you will need to test & record those particular changes to your "benchmarks" as well, to maintain a "constant" of factors(parameters) for your results to remain consistent as well.

Once again, G'Luck!
:)

[JBinMN]

Just a note on "lots" for those benchmarks...

Eventually you will run out of those benchmark rounds, but if you make sure to remember when you get down to the last hundred or so, to begin to test a new "lot" of rounds with the old ones to establish a new benchmark load. That way you can verify that the new ones are consistent since they were tested against the old benchmark ones.

Meaning, lets say you used 500 Eley match grade .22LR rounds for your benchmark load, and you are down to your last 100 Eley rounds. Those loads averages about 1200FPS +/- and were consistent. Since it is time to establish a new benchmark load & perhaps you are not able to find those same type of Eley rounds, you have to choose another type of round. You might decide to use Remington or Federal, or even CCI, etc. instead of the Eley ones, and maybe perhaps even another caliber or something, but regardless of what you choose you should start establishing the new benchmark using the old benchmark as a "standard" to compare the new ones for the future.

If the new, let say, 500 CCI rounds run at approx. 1150FPS +/- for those rounds as compared to the Eley ones you previously used, then you record that change in velocity and establish that 1150 +/- as the new benchmark.

If by chance the "spread" in velocity of those new rounds is more than you like, such as 1150 average, but you get some that are 1100 & some that are 1200, for a range of 100FPS, you have quite a large range of velocity. It would be much better to have a range of 15-25 FPS +/-, or less, & so perhaps you want to test a different type of ammo mnfr product to get an ammo that is a bit more consistent, before you run out of the old benchmark rounds.

But once you have used the old benchmark to establish the new one, if you consistently use the same "lot" of ammo for your benchmark, you can "know" you are getting consistent testing of your chrony each time you check it before you test other things/rounds/calibers.

OK, I am done now. BTW, if ya already knew all of this, then maybe someone else might find the info worthwhile.
Or, someone can come along & try to give me some crapola about how long my posts are & other ******** like that... Either way, I was trying to help.
;)

[country gent]

I too used a test firearm when setting up my pact professional I used a rws1 side cocker pellet gun and a "select" lot of pellets, nithing special about them just the same lot# for the batch of 1000. 10 shots over the screens proved the set up was good.
Light, smoke ( from powder lubes ), distance and battery charge can all affect readings. I would try a new set of batteries with the load and see what you get reading wise. Light can be controlled with diffusers to break up the bright direct glares. A piece of 1/8" plexiglass lightly sand blasted to frost it works good. I like about 8" over hang all around the unit. This keeps loght much more even. Last is to check ad clean all connections so they have good contact. A weak contact may slow the signal affecting readings.

[lar45]

Yes, try a new battery and report back please.