The Mighty .32ACP and Others

[BLTsandwedge]

Saturday I set up the chronograph and collected around 25 data sets- from .45AR to .22LR. I'm just now beginning to measure external ballistics, so my methodology isn't tight yet. Each data set includes at least 10 rounds measured in feet per second, and measurements are recorded on a Shooting Chrony Beta @ 10'. I ten-key each data point into an Excel workbook and use the existing formulas for STDEV and AVERAGE, the latter being a string's mean average. Even though I'm new to thys, it's a kick- using statistical analysis adds another big dimension to the hobby.

One general observation I came away with is that the smaller the cartridge case (.22rf aside) the greater the standard deviation from round to round. As an example, a 10mm loaded with 7.9g Power Pistol under a #401638 produced a mean average velocity of 1,222.22 FPS with a standard deviation of 5.1 FPS. To the other extreme, a .32ACP loaded with a Tru-Cast 71g LRN over 2g of 700X produced a velocity of 795FPS with a standard deviation of 41.1FPS. That's a 5% +/- deviation factor for the .32 compared to a .04% +/- for the 10mm. As the case volume fell, the shot-to-shot deviation increased. This was suggested even with .32 factory ammo- the same 35 to 40FPS standard deviation was present in Remington and PMC.

Having said that, I have my doubts that we can say "the smaller the case, the greater the shot-to-shot deviation will be." Or, in general terms, can that be said? I measured five different brands of .22LR; standard deviations ran from 13 to 28- roughly the same as mid-capacity rounds such as .40 and .45ACP/AR.

I've nowhere near enough data collected to make any assertions other than individual loads used in individual guns. But, for the technically inclined folks on the board, what has been your experience with small calibers and STDEV?

Next BIG question. Has anyone tightened their methodology to the point of being able to run a Pearson to correlate the effect of one variable adjustment at a time? That, to me, is likely the end-game in ultra-fine tuning of a handload.

Enquiring minds want to know...........

Thanks

Tom

[BLTsandwedge]

To further the thought- do we assume that the smaller the shot-to-shot standard deviation, the more accurate the cartridge/load?

[35remington]

No. Low SD's often have nothing to do with good accuracy.

Your SD for the 10mm was 0.417 % of average velocity, not 0.04%. Remember to multiply by 100.

"One general observation I came away with is that the smaller the cartridge case (.22rf aside) the greater the standard deviation from round to round."

That's not the conclusion I have come up with. On the contrary, quite the opposite.

Usually, as case volume falls, and assuming all else remains the same, SD's will decrease. The powder has less room to move about and this tends to lower SD's simply from reducing powder position variation.

You're comparing the case capacity of 32 and 10mm without taking working pressures into account, which throws off your comparison and makes it apples and oranges. The 32 operates at less than half the pressure of the 10mm.

In the 45 ACP, for example, the lowest SD's within normal working pressures are found with the heavier, more deeply bullets.....less room for the powder to wander, less velocity variation from powder forward versus powder rearward.

[runfiverun]

in the long run and in different conditions i think the lower deviation will prove out to be the winner in the accuracy dept.
as long as the load is coming out the bbl in the proper node i.e the top or where the node is at a static point.
if you are in the middle accuracy probably isn't so good to start with.

[Bill*]

Maybe the smaller cals simply have a greater percentage of variance?
For instance, a tenth of a grain is 5% of a 2 grain load, yet that same tenth of a grain is only 2% of a 5 grain load. I expect loading to 1 hundredth of a grain would even things up. I'm not sure you could even get that precise unless your powder was like flour. Also, as the scales rounds to the nearest tenth you could theoretically have 2 grain loads that are 1.95 and 2.05 side by side that scale the same. This difference would be less (percentagewise)for larger caliber (heavier) loads

[sagacious]

I have favorite a 45Colt recipe that uses a modest charge of Bullseye and a 200gr bullet cast from acww's. Shot from my Marlin 1894, the chronograph reads 1333, 1333, 1333, 1334, 1333fps etc etc etc. The standard deviation is virtually zero.

Bear in mind that this is a large case with a fairly light-for-caliber bullet and a small powder charge. Even the target 22lr ammo that I use to check the chronograph never shows that level of consistency. I have some 45ACP loads that are so accurate they're almost boring, but they don't show the same miniscule velocity deviation.

I would humbly suggest that the test made in the opening post of this thread is not comprehensive enough to draw any general conclusions from, and one must always be vigilant that coincidence will sometimes offer support for an incorrect theory. However, this type of testing is what leads to more knowledgeable reloaders and better handloads, so keep on keepin' on. :drinks:

[BLTsandwedge]

Thanks 35, great input.


No. Low SD's often have nothing to do with good accuracy.

Your SD for the 10mm was 0.417 % of average velocity, not 0.04%. Remember to multiply by 100.

Quite right. I'm too accustomed to reading absolute values as opposed to percentages!

"One general observation I came away with is that the smaller the cartridge case (.22rf aside) the greater the standard deviation from round to round."


That's not the conclusion I have come up with. On the contrary, quite the opposite.

Usually, as case volume falls, and assuming all else remains the same, SD's will decrease. The powder has less room to move about and this tends to lower SD's simply from reducing powder position variation.

You're comparing the case capacity of 32 and 10mm without taking working pressures into account, which throws off your comparison and makes it apples and oranges. The 32 operates at less than half the pressure of the 10mm.

In the 45 ACP, for example, the lowest SD's within normal working pressures are found with the heavier, more deeply bullets.....less room for the powder to wander, less velocity variation from powder forward versus powder rearward.

Sounds feasable- how does pressure come into play in relation to SD? Does more pressure equal a decrease in shot-to-shot velocity deviation? In addition, is it possible then that cases like the tiny .32 are less tolerant to inexact powder charges- thus causing the big SDs in my (limited) observations? This stuff is very interesting!

Tom

[BLTsandwedge]

Maybe the smaller cals simply have a greater percentage of variance?
For instance, a tenth of a grain is 5% of a 2 grain load, yet that same tenth of a grain is only 2% of a 5 grain load. I expect loading to 1 hundredth of a grain would even things up. I'm not sure you could even get that precise unless your powder was like flour. Also, as the scales rounds to the nearest tenth you could theoretically have 2 grain loads that are 1.95 and 2.05 side by side that scale the same. This difference would be less (percentagewise)for larger caliber (heavier) loads

That's my question as well.......

Tom

[mpmarty]

I believe a lot of the variables are due to combustion efficiency at higher pressures or lack thereof.

[35remington]

Boy, you ask a lot of tough questions, and I'm not sure I have all the answers. What I'm speaking of is empirical evidence, besides that gained from reading the work of others.

It's possible to have high pressures and yet have high SD's because the powder doesn't occupy much case space and is position sensitive. In that case the high SD's result from powder positioning that causes variance in the pressure even though the pressure is up there.

If I really want to see low ES try a fast powder, precisely weighed or metered, with a heavy bullet in a small capacity case at high pressure. Then they're really low. But I'm also assuming a full or nearly full case of powder, or a powder so fast that minor changes in position in a small case don't matter much.

So I don't think I myself can narrow it to pressure alone without considering how much airspace there is in the cartridge. I can tell you that with the faster powders such as the shotgun/pistol types velocity variation is minimal compared to a slower powder in some instaces......most recently this was brought home to me in comparing Unique with 4198 in the 25-20. Unique shows less velocity variation with variations in powder charge position, even though pressures are equal or lower than with 4198, and even though the airspace is greater with Unique. And this is taking the differences in velocity into account, as well.

I suppose the charge variation thing is possible......for me to know if that's a factor or not, I'd have to know just how much your charges vary!

I do know that in small cases using small powder charges, large flake powders such as 700X or Red Dot do not meter well enough to avoid a fairly high charge to charge weigh variation. In fact, below about 3.5 grains, my Pro Auto Disk will dispense the occasional squib charge rather than a full charge about every 60 shots or so, which is why I stopped using charges of below 3.5 grains with large flake powders in the PAD.

With small capacity cases using pistol powders, consistent charge weight is a tricky thing to accomplish unless the powder meters well.

[BLTsandwedge]

Great stuff. In my mind the equipment and technique I use will not allow us to separate variables enough to ultimately apply or create "if-then" arguements. However, we can get close enough to have a general working idea. Starting with variables we can control- bullet weight/type and powder weight/type we can see what happens to SD when we are as precise with our weight measurements as possible. I may find that precise measurements of powder in a .32 case brings SD down substantially. It may not affect SD at all. Same thing with COL and bullet weight.

Perhaps that's the limit of my capabilities. We certainly can't include factors such as relatve humidity, powder lot size, chronograph personality. I'm happy chasing generalizations though.....as long as it puts me at the range............

Thanks all

Tom

[runfiverun]

with the smaller powder amounts often going volumnmetrically instead of weight will work.
in my 32-20's i reform for my 30 carbine revolver it is much easier to use a scoop and go with that volumn rather than trying to hit an exact weight through a machine.

[35remington]

Volumetrically is my problem.

When the round cavities get too small in diameter, the flakes bridge over the small opening rather than fill it correctly.

Had I weighed every charge, then there's no problem with the larger flake powders, but I hate to weigh charges for the small pistol size cases.....it's too slow for me.

[JIMinPHX]

In my experience, I generally get smaller speed deviations from powder charges that leave less open air space above the charge, assuming that the same powder is used in each case. Compressed charges tend to be very consistent.

I've also noticed that certain powders tend to give much less deviation than others do, H-110 being the hands down winner in that category.

[jonk]

While interesting, I've yet to find a .32 that shoots well enough to matter. As long as the bullets don't keyhole I can't really tell the difference between a great load and a crummy one. Perhaps if I had a ransom rest or similar...

But to the SD question. I've gotten SD of 8-9 fps with cat sneeze loads and 8-9 fps variation with full tilt jacketed loads in the same cartridge; and 200 fps variation as well! It depends on powder combustion.

700X is fairly fast, yes, but in the teensy tiny .32 ACP I use bullseye or red dot only- the very fastest easily found. 700 X is rather far down the chart actually, by comparison.

I'd assume you simply aren't getting enough pressure with only 2 grains to burn it completely. I'd switch to a faster powder and try this again.

[twotrees]

Is it a "True" round to round variation, or is your Crony just nor "seeing" the smaller bullets as well?

22 Match grad ammo is VERY consistant and still hard to read on mine.

Just a thought.

[BLTsandwedge]

While interesting, I've yet to find a .32 that shoots well enough to matter. As long as the bullets don't keyhole I can't really tell the difference between a great load and a crummy one. Perhaps if I had a ransom rest or similar...

But to the SD question. I've gotten SD of 8-9 fps with cat sneeze loads and 8-9 fps variation with full tilt jacketed loads in the same cartridge; and 200 fps variation as well! It depends on powder combustion.

Lol- actually it's general inference (or lack thereof) that the .32 may perhaps point to. My test gun is a Walther knockoff made by CZ. At 15 yards I'm impressed i.e. 2 1/2" groups offhand/two-hand hold with certain loads, noably the little 60g Speer Gold Dot. But there's huge SD with every load I tried, factory included. In contrast, the S&W 610 provides outstanding accuracy at 25 yards with very, very small shot-to-shot SD. My original question based on this comparison- is SD a component of accuracy- was answered to a degree by the board- recognizing the lack of further comparison. We all agree that I don't have enough data to provide for any generality; I'll be correcting that, one variable at a time.

Correct me if I'm wrong folks- don't Lyman, Speer et al identify the most potentially accurate loads in their books by comparing standard deviation? If so, that tells me the experts consider SD to be a key factor in accuracy. The spinoff question- can we automatically assume a cartridge featuring a small case volume will be inherently less accurate than a cartridge with a much greater capacity? If so, is that why the .32ACP (and others) have not shown up in bullseye competition with any degree of popularity? If case volume is one predicator of accuracy, why is the 22LR world-renowned for accuracy?

I believe that SD is a factor in accuracy; that it can, when considering some cartridges, be a reasonably accepted generalization (how's that for a BS hedge?). Like we do with any theory is to go about disproving it. If I can't disprove it, then I want to know when it applies- and why. I'd be delighed to be wrong prvided I know how and why.

Is this information of use? What's on the other side of that hill?

[JIMinPHX]

If you're having problems with the Chrony not seeing small boolits very well, then try shooting down closer to the sensors. If you shoot about 1-2" above them, they can see something as small as a BB. Of course, there is the obvious risk to the equipment that you do need to consider. Lighting matters too. Bright days with sky screens or cloudy bright days without sky screens work best. Indoors or in the shade is always tough.

[runfiverun]

it is funny the 22 would be considered accurate with the heeled boolit it has and all, it seems to fly in the face of whats right.
however what it does have going for it is consistency.
consistency in priming compound,in rim thickness[headspacing],in powder weights [i bet not so much]
in boolit weight,and case length/case dimensions.
having consistent velocities with the chosen powder being consumed totally through heat and pressure before the end of the bbl is where i believe your accuracy comes from.
if you have a consistent muzzle pressure from shot to shot you will be affecting the boolits exit the same way each time.
that and where it is leaving the bbl in the sinewave pattern will and can affect accuracy.
what you are doing is timing all these events to occur at the same exit time as close as possible.
it all starts with the ignition of the powder.
neck tension,powder composition.how full the case is [position] and brisance/ingredients of the primer all have an effect on just this one thing.
in your 32's case a faster/slower powder or a different primer could be all thats needed.

[CB Hunter]

BLTSW,

Some observations and experience.

1) 10 rounds is not a statistically significant sample, although it will give a good approximation.

2) The results you get, even with the same gun and batch of ammunition, will vary day-to-day, even at approximately the same temperature.

3) Results will vary with the same ammunition, fired on the same day, when shot in different guns. This isn't even logical in that you can see a similar ES and have a higher or lower SD, or the converse, when strings are shot in different guns.

Finally, doesn't the Shooting Chrono Beta calculate ES, Mean and SD for you, their web site seems to indicate it should? I guess I may be spoiled with my Oehler 35P.

[Dave C.]

I am willing to collect data for a small case. All I need is a match grade heavy barrel bolt gun with a 32X scope and a boolit mould to go with the NOS carbide dies that I had given to me years ago but I never used yet. So anybody got a rifle like the one listed above chambered in 25ACP?

Dave C.

[BLTsandwedge]

BLTSW,

Some observations and experience.

1) 10 rounds is not a statistically significant sample, although it will give a good approximation.

2) The results you get, even with the same gun and batch of ammunition, will vary day-to-day, even at approximately the same temperature.

3) Results will vary with the same ammunition, fired on the same day, when shot in different guns. This isn't even logical in that you can see a similar ES and have a higher or lower SD, or the converse, when strings are shot in different guns.

Finally, doesn't the Shooting Chrono Beta calculate ES, Mean and SD for you, their web site seems to indicate it should? I guess I may be spoiled with my Oehler 35P.

CB,

There's no doubt to your first point. There's only enough there to ask a question- and pique curiosity (mine anyway- doesn't take much for simple minds to be amused). Nor is there doubt as to the variables you mention. Re the Shooting Chrono, yes it will provide for some basic data such as ES & SD. I prefer to key the raw data into Excel. At some point I'll have enough raw information to define samples and start looking for linear correlation on the variables I can (somewhat) control for. Excel is surprisingly capable of running correlataions and establishing confidence.

One side note- you get what you pay for. The Shooting Chronny is basic and seriously fussy. It does not tolerate changes in ambient light. The sky screens are held in position by tension- they're prone to be flung off the machine and into the next borough when their two-piece rods slip. But, for less than $100, I'll limp along with it.................

Tom

[Wayne Smith]

I don't know this for a fact, just enough information to suggest that the .22 is not a good comparison. I think if you look at all the research time, money, and effort that has gone into each cartridge I'll bet that the .22 outstrips all of the others except perhaps the 30-06. The .22 is the only cartridge that has been a competitive round for over 100 years.

[BLTsandwedge]

I don't know this for a fact, just enough information to suggest that the .22 is not a good comparison. I think if you look at all the research time, money, and effort that has gone into each cartridge I'll bet that the .22 outstrips all of the others except perhaps the 30-06. The .22 is the only cartridge that has been a competitive round for over 100 years.

Valid point. I hadn't considered that...........