[Kosh75287]

I've only chronographed two loads with my new chronograph, so the issue I describe MAY only be characteristic of those two loads, BUT...
How large does the standard deviation get, as a percentage of average velocity, before you conclude that the load is inconsistent?
For example, if I have a load in .357 magnum that averages 1260 f/s + 63 f/s, then that's a 5% standard deviation. I'd continue to look for better but, for a pistol round, at pistol distances, I could LIVE with this. This same amount of deviation in a 3000 f/s rifle, on the other hand, seems so large as to probably render the rifle too inaccurate to be depended on for much of anything beyond shouting distances.
I'm ALSO aware that low variation of velocity is no guarantee of good accuracy. It's darned difficult, however, to obtain good accuracy without it.
We all HOPE for single-digit S.D.s, but must often settle for low double-digit S.D.s. At what percentage do we decide that a certain load is consistent enough for use, or not?

 

[grcsat]

My info is a bit old so maybe there is a newer measure

15-25 fps very good quality ammo for the average rifle and under 10 for a target shooter. ( Chinese ammo 😁😁😁😁 100-150 fps )
The best I have ever gotten is 8 fps for my bench rest 243 target ammo. Note. this is with bench rest dies ect. And done with a 1980s chrony.

 

[Kosh75287]

Thanks. That gives me something to aspire to.

 

[PRR1957]

My experience with chronographs is the lesser expensive ones are not that accurate compared to say one of the high end Orhler chronographs. I used be part owner of a Chrony back in the early 1990’s. One day at the rifle range where I was conducting a load ladder test with the Chrony. Set up a few benches over from me, another guy had an Oehler. He and I got to talking about accuracy of are chronographs, and I asked to fire ten shots across his and found that with his Oehler chronograph shown a lower SD, plus it recorded every shot were my Chrony would miss recording at least one shot out of ten. Both are chronographs where set up under the same lighting and temperature conditions. Years latter I worked for an Arms manufacture that had an Oehler, and I was able to compare the Chrony again and it is a cases of you get what you pay for. The only other chronograph that I know that is as accurate as an Oehler is LabRadar.

I am not suggesting that your chronograph is cheap, but in my opinion, if you do not have an Oehler or a LabRadar the lesser priced brands to me are only good to give you a ball park indication of what your firearm and its load is doing. Also. Don’t get get hung up on the SD. I had one rifle that had a high SD, but still shot five shot 1/8 MOA groups at 100, and 200 yards, but that kind of accuracy is more of a product barrel harmonics and how that influence bullet stability and the particular bullet design and primarily its BC.

I should add, is that most of chronographs detect the bullet passing over photosensors, and when used out doors, the ambient light can cause errors such as if the chronograph is illuminated with Sun off to one side and shining on the photosensors and not passing through the diffusers, or if it’s a sunny day with scattered thin clouds. Even the expensive chronographs such as an Oehler can give erroneous readings if the lightning and temperature conditions are not optimal or consistent. The only chronograph that seems immune to variable atmospheric conditions is a LabRadar, but those are $550+ units, even that brand can be fooled at times. Your best bet is to try and maintain the operational use under as consistent conditions as possible with temperature being a factor that with some chronographs suggesting a certain temperature operating range.

 

[grcsat]

I must agree with PRR1957.
Don't chase the SD , chase the 1MOA.

My results are a one time thing , with old equipment (new at the time ) and will most likely never happen again.
I still have the printout only to show people that I used to belong to the " under 10 club "

 

[noylj]

You know, the TARGET always tells me if the load is inconsistent.
I have seen very low S.D. loads that were very poor in terms of group size and high S.D. loads that grouped very well.
A chrono is no substitute for real targets/groups size.

 

[Kosh75287]

I agree that on-target accuracy is more important than shot-to-shot velocity uniformity, but I am trying to consistently exceed a minimum velocity (1070 f/s), should these rounds be used in competition. I don't need a good day in competition to be wrecked by my rounds dropping through the velocity floor. Since I tend to serve as the "poster child" for Murphy's Law, I like to take as much of the "whatever CAN go wrong" out of the equation.

A MAJOR part of the variance that I'm encountering MAY be due to reloading technique, though I was fairly meticulous with everything. I don't know what I would have done differently. I used a powder measure, which I checked regularly. I used Accurate #5, which is HARDLY known for metering badly. Projectiles were from a reputable firm, varied in weight no more than 1 grain in 158 grains (all but 3 in 500, far less), and seating depths are uniform across each caliber (.38 Spl. & .357 Magnum). Headstamps were varied, but sorted & shot together. I excluded any WCC headstamps, since they tend to have heavier webs.

More later.

 

[Kosh75287]

I shot 9.2/Accurate #5/158 gr. FMJFP in .357 Magnum cases from a 6" S&W M28 and from a 4" Ruger Police Service Six. Velocities, respectively, were 1160 + 49 f/s and 1148 + 29 f/s. There was a .38 Special load, using same propellant and projectile. The charge weight was well out of the .38 Spl. +P range, so I'll refrain from mentioning it, here. Velocities, in the same order, were 979 + 36 f/s and 917 + 97(!!!) f/s. I have a feeling that some of this was "operator error", but I have gone over it several times and cannot IMAGINE what I should have changed.
All "conditions" were 18 rounds each, fired from a rest, between noon and 2 p.m. The temp was ~76 degrees F, the weather was partly cloudy to slightly overcast. The chronograph was a 12.5 measured feet from the muzzle of each revolver (plus or minus 3"). The chronograph battery was fresh out of the package. No other experimental confounds were detected.
I'm not unhappy with the .357 Mag performance (and it's more accurate than I am), though I may see if one or 2 tenths of a grain more or less may narrow the variance. The .38 Special, however, is a head-scratcher. I'll have to re-shoot those, just to see if I can duplicate the variance. I may go up 0.2 gr. just to see what happens. I checked primers and there were no signs of severe flattening in either condition.

Ideas, anyone?

 

[noylj]

Ahh, meeting power factor. THAT is much different than trying to guess accuracy based on S.D.
This becomes a competition question and the answer is: How are loads monitored at the match you go to? Does the extra velocity slow you down or hurt your accuracy enough to matter? Can you bring a couple of different loads to account for chronograph and weather effects and choose which to use? Is it worth sailing as close as possible to the floor of power factor?
Again, though, this is really only a competition issue of gamesmanship.
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Reloading to Meet Power Factor with Confidence!

I still see a lot of people wondering why they fail to meet PF at a match. If you just add a few extra power factor points, now you know what can happen. The bottom line is that velocity is random in nature and the BEST way to understand and manage it is to use statistics. You don’t need to have ...

forums.brianenos.com

 

[PRR1957]

Just an idea, but what is the cylinder gap on the two revolvers. Production assembly line firearms such as your Ruger and S&W are not custom shop tuned revolvers. Cylinder gap can vary between one cylinder chamber and the 180* opposing cylinder chamber, assuming they are six chambered cylinders. Try cleaning all the carbon from the face of the forcing cone and the front the cylinder, then check the cylinder gap on all the cylinders chambers. You mite discover that cylinder gap could be say .003” and the 180* opposing cylinder gap is say .005”+/-. I had a Ruger Super Blackhawk that had variation in its cylinder gap. So this something you mite want to check with a feeler gauge set.

Another variable in your ammo in that you are not using cartridge case all from the same manufacture. As an example. When I am loading precision ammo, I try to acquire cartridge case not only from the same manufacture, but the same production batch so as to remove one of a multitude of variables. If I run out of a certain gunpowder or primers and to replicate the load with the same type of gunpowder or primers, but they are from a different production lot #, I will retest said components before committing to load a large quantity. Here is a recent example that I ran into loading 1000 rounds of 223 Rem. for a friend who supplied me with four pounds one pound cans of Hodgdon, Benchmark. Two pounds were of one lot #, and the second two pounds were from a different lot #. One lot # bulked differently by .20 grains. Same power brand and type but different production lots. So for the second two pounds I had to retest.

 

[Kosh75287]

Ahh, meeting power factor. THAT is much different than trying to guess accuracy based on S.D.

When you write things like this, I instantly get a "visual flash" of Don Adams, on "GET SMART" saying the very same words. "Ah, yes! The old (insert cliched espionage deception here) trick!"
If I'm usure of the source of variation (chronograph, or firearm or handload), how am I to be confident about how to compensate for it? If MY chronograph is biased to the high side by 4%, and the match chronograph is biased to the low side by 4%, then the load that I concoct, showing a PF of 174.9 (6% over minimum indicated, 1.76% in actuality) on my chronograph comes in at 161, and I am sca-rooed.

How are loads monitored at the match you go to?

Excellent question. I'm sure it varies slightly from one match to another, which is why I'm trying to isolate and quantify the variance in MY machinations.

Does the extra velocity slow you down or hurt your accuracy enough to matter?

I don't know. How much extra velocity do I REALLY have? And how does one define "enough to matter"?

Can you bring a couple of different loads to account for chronograph and weather effects and choose which to use?

In the days before COVID, perhaps. But as you have been so fond to point out to me, the current pandemic has crimped supplies to an unprecedented level. I'm not sure how many rounds are usually fired, per competition, but producing and transporting two or three times the number required seems problematic.

Is it worth sailing as close as possible to the floor of power factor?

At this introductory stage of my competition experience? Perhaps not. Later on, who knows? As the competition skill levels elevate, the margins between 1st, 2nd, and 3rd place narrow considerably. I'd rather do my homework now, than later.

ADDENDUM: The thoughts about the flash gap varying among the individual cylinders in each revolver is certainly worth checking. Good idea.
I'm sorry that I didn't make it at all clear what I meant by "sorted and shot together". The .357 loads for each revolver were all loaded in Winchester nickel plated cases. The .38 Spl. loads shot in each revolver were in unplated R-P cases. Incidentally, there were no "splits" nor obvious failures of the .38 special cases which (I'd HOPED) might account for some of the very low velocities obtained in the 4" Ruger Police Service Six.
All the AA#5 used was from one bottle, though it may have been older than I thought. It was not malodorous nor did it exhibit clumping nor other obvious signs of decay/degradation. I have another unopened bottle of AA#5, so I may try this again, just to see what results I obtain from it.
Thanks for the ideas!

 

[ms6852]

You know, the TARGET always tells me if the load is inconsistent.

^^^^^This is exactly my train of thought. When I develop loads I do not use a chronograph. I like to shoot 5 shot groups at 200 yards with various loads and the load that gives me the best 5 shot group at 200 yards is what I load. Only than do I use a chronograph to establish velocity of the round so that I may work on a drop chart at various distances.

 

[Kosh75287]

As I thought I'd previously said, I understand and agree with letting the target tell me what works and what doesn't, WITH RIFLES. Assuming I've correctly matched the rifle to the task of interest, even a slightly attenuated load will have enough "oomph" to complete the mission.
In the case of these revolvers, however, a certain ballistic minimum is required. If the load that makes major power factor also groups 5 or 6 rounds inside 2" at 50 yards, that's wonderful. But I'll settle for considerably more dispersion than that, if the load makes major by a comfortable margin and with a suitably small s.d.

 

[noylj]

Go to Brian Enos forum. They've dealt with this for years. Back in my day with ipsc, 6.0gn Unique and 200gn L-SWC was well over 175.

 

[Don Fischer]

When I started in reloading, we didn't have chronographs, we had hole's in a target! Today I do have a chronograph, h*ll I'm a handloader, it's required! Know what I'd rather have than an 10 fps SD? A half inch group!

 

[Kosh75287]

Back in my day with ipsc, 6.0gn Unique and 200gn L-SWC was well over 175.

Do you have such a load for .357? I may be shooting THAT as much or more than my .45 ACP (for which my "Major" load is very similar) in competition.

 

[noylj]

I've never chronoed .357