Can anyone offer up a valid reason for the velocity variance of given loads.?? Before I left for my medical thing at one point, I did some testing. Five shot test showed 21.2 variance in the selected loads. All things being equal, what would cause this. These hand gun loads were carefully crafted one at a time. Just something I have been thinking about aas I have very little else to think about these days. Sure will be glad to get home next week. Thanks for your input.

Check out "The Perverse Nature of Standard Deviation":
https://www.shootingsoftware.com/ftp...%20of%20SD.pdf
Variance means very little on it's own.
5-6 shot variance or even SD means little.
Also a particular SD only applies to that load.
SD of 10 in one load has a different meaning than SD 10 for a load with a different average velocity.

What the target looks like is what you want to maximize.
I have collected a lot of data and targets and good targets and good SD correlate only some of the time.
You know what they say about statistics (lies, damn lies, ...).
The predictive powers only become apparent with large data bases not groups of 5 or 6.

Most revolver loads are only partially full of powder.
I believe this to be one of the major sources of velocity variance.
But after years of playing with some fillers, I decided it was not worth the effort as little improvement was noted
and while some targets were impressive it was not a universal effect.

"Mic" McPherson has suggested pushing the bullets further down in the case to mitigate this problem but I have never had the time to pursue this much.
This also goes against what some riflemen do when setting the bullets to (just) touch the rifling to center the bullet and eliminate freebore or bullet jump.
It's an interesting idea from an expert however.
Metallic Cartridge Handloading: Pursuit of the Perfect Cartridge by M.L. McPherson

Collecting chronograph data is a worthwhile venture, but I use it mostly to try and calculate the actual pressures involved and keep out of trouble.
Feeding this data back into QuickLOAD makes it more accurate.
Also a totally horrible SD (like 10+ times worse than expected) may indicate a problem in ignition or just a bad recipe.
For instance I have given up on using 1680 in the .445 because a combination of poor targets and a lot of blowback
(poor cartridge seal) is also attended with variance in the 100's fps and SD in the dozens.

Variance and SD are not completely worthless but are given much more value than they deserve especially when it comes to revolvers IMHO.

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NEMO
"Everything 44"

SD and ES are popular topics with today's Internet folks and they're often very concerned about variance in the figures. If you're getting good accuracy, pay no attention to the numbers. At best, they're a measure of consistency. Many other factors affect accuracy.

Target accuracy can happen with FPS and ES with bullets and barrel lengths.

I have weapons that are accurate with target loads and factory Dup. loads at full pressures. It just depends on the ammo and weapon used.

As for ES..........
I have several loads in my 38, 357 and 9mm's that shoot well with loads that have just a 12-30 ES and I also

have loads that are very accurate that have a ES of over 120, which I still don't understand.

Just one certain load shot on different days with temperature and even humidity changes, can change your numbers.
Maybe this is why you can have good days and bad days at the range?

I would not worry too much over this, it will give you gray hairs.

How are you able to calculate pressures from chronograph data? Please explain. Are there formulas that you use?

SD's and ES are much better applied to rifle than handgun. Some of My most accurate loads in My 57 have horrible SD and on in particular has extreme spread of 188, and yet prints 24 inside the 9 ring at 50 yards. Thats about 2 1/2 inchs.

I too, use my chrony to look for higher pressure loads. High velocity normally equates to higher pressure, so if I'm getting 300 fps more than the max load listing in my manuals my loads may be too high (yeah, I know the manuals list results from different barrel lengths than mine, different exact components and the use of universal receivers). It is not exact, does not tell me pressure, it only tells me the load is approaching max or may be too high...

These are older guns and while velocities can indicate pressure I do look at a couple other things. Target, etc., a bit of unburned powder can indicate a bit more power in needed but these guns do not need plus P loads. I just dont want to over do it. I find it amazing the things you can think about when you have so much time on your hands. My main concerns use to be, does the load work?

A chrony gives you the fps to help your weapon reach factory speeds and allowable pressures.

Generally, a slower powder will get higher fps with lower pressures but this is not always true !!

I have had slow powders max out before reaching fac dup in some of my test, so you do need to use care, with all the components out there, that can be used.

Stay safe.

I use the QuickLOAD internal ballistics program.
It comes with a fairly lengthy article about how it works and the limitations but they are understandably shy about divulging the exact mathematics.

Chronograph data is only a part of the input.
It's feedback actually.
Yes it's an estimation but the best one there is short of military software costing $thousands.
Once I get the program to predict velocities that are actually happening, I trust the pressure predictions to a certain degree.
The program itself claims to be more accurate for bottleneck rifle cartridges and higher pressure in the 50-60 kpsi range.
IMHO it usually over estimates the pressure for revolver cartridges when I compare the results to published numbers in reloading manuals and articles.
I believe it also over estimates the fill ratio as well for the powders I use.
This is fine and keeps me out of trouble when developing an untried load combo particularly in .445 where published data is scarce.

I hope that answers your question.
QuickLOAD is definitely worth the money but does take some time to train both the user and the program itself.
I keep a little salt around as well when I find myself getting too serious with the numbers.

This load performs exactly as predicted.
I tweak the case capacity and the Burning Rate slightly until it does.
Then I trust the ladder predictions better.
I would not shoot these in a revolver but I do in the Encore.
I limit break and lever action rounds to an arbitrary 45kpsi.

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NEMO
"Everything 44"

I'm not even sure that bench rest shooters obsess about velocity. As far as I have been able to tell, informed concern about variation of velocity starts at about 300 yards. Before that, find other things to worry about.

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AKA ImprovedModel56Fan

For today's compulsive ES and SD enthusiasts... if you want to get numbers with the smallest amount of variance in a bottleneck rifle cartridge, standard or magnum, use a slow powder and a compressed load. You'll be amazed at the figures, but they are no guarantee the load will shoot with decent accuracy.

IME, that's pretty dam low ES for a handgun.

As said earlier, the most likely reason is the relatively low case fill compared to rifle. This allows the powder in each cartridge to be positioned differently depending on how stored, loaded, and/or where in the string it is fired . . . and what you did with the handgun in between shots. This affects the burn rate.

Also "carefully crafted" doesn't tell us whether you verified equal neck tension across different cases. In rifle, that's often done by turning case necks to prevent oversizing due to thick neck walls, and either leaving carbon inside the neck or lubing to ensure easy release. This affects pre-launch pressure buildup. Such steps are not usually taken for handguns because they are largely irrelevant to group size over distances normally shot.

There are perhaps other reasons that can be pursued by looking at what many rifle shooters who carefully craft their ammo routinely use.

But I repeat, IME your ES is pretty dam good.

Force = mass X acceleration along with the equations for velocity, distance, time and acceleration.

KNOWNS: chronograph velocity, barrel length, bullet weight.

Ignored factors: Perfect gas law, changing volume, high temperature & high pressure mass flow of expanding powder gas.

At 12:40 AM I'm not looking for velocity, time, acceleration equations I haven't used in 40 years. Some place in the distant past there was a classroom discussion about firing 16" battleship guns. In Physics for Engineers, a Navy guy who was on the New Jersesy (near Viet Nam) asked a question and we were off to the races. The know factors were impressive; bullet weight in thousands of pounds, barrel length in feet, fired distance in miles.

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S&WHF 366

A-Square's handloading and rifle manual "Any Shot You Want" includes some data for the 105x608mm tank gun.
A picture of one firing at night is on the cover.
One of the most entertaining manuals out there if you are a big bore nut.
The author developed loads for that gun and others during his military career after which he became a big bore shooting guru.

He uses this large caliber to show that pressures in gun cartridges are all about the same no matter the size.
Pressures range from 24 to 60 kcup for the various projectiles listed.
His writing style is highly amusing IMHO:

"I am sick to death of the pinheads that come into the booth, stick their finger in the muzzle of a rifle in .500 A-Square or .470 Capstick
(I'm not sure what they think they are measuring but I've got a good suggestion for another place to put their finger),
utter some comment like "Look at the size of that hole! Why the pressures must be horrendous, that rifle will blow up"
and then dance back into the aisle as if they had just revealed some immutable truth.
They couldn't be more wrong."

"Please don't ask A-Square company to make you a rifle in 105x608mm.
Sorry we won't do it"

HEP-T projectile 24.8 lbs 60710 powder 96.8 oz 2400 fps 24 kcup
APDS-T projectile 12.94 lbs 67878 powder 197.6 oz 4875 fps 60.1 kcup
TPDS-T projectile 8.54 lbs 69584 powder 159.3 oz 5050 fps 51.9 kcup

Art Alphin (Mr. A-Square), Finn Aagaard, Craig Boddington, Gary Minton, and Terry Wieland wrote the chapters in this book.
624 pages of hunting happiness. Recommended.

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NEMO
"Everything 44"

Well I was always happy things worked and hit what they were supposed to. These days, with more time, maybe too muchon my hands I have started being concerned more with velocity than much else. I am thinking if five rounds are loaded, and all treated the same, the velocity of said rounds should be pretty much the same-- even with any given box??? Need I rethink all this??

[QUOTE=Nemo288;140886285]Check out "The Perverse Nature of Standard Deviation":

"Most revolver loads are only partially full of powder.
I believe this to be one of the major sources of velocity variance."

I couldn't agree more with Nemo288. I loaded some .32-20 rounds a while back and launched them over a chronograph and was startled by their velocity variance. Given the powder charge did not come close to filling the case I became curious. I shot two six shot strings; one after shaking with muzzle down, and one after shaking the revolver muzzle up, before each shot. With the powder mostly towards the projectile the average was 540 feet per second. With the powder mostly nearer the primer the velocity averaged 820 feet per second. I viewed this as an astonishing difference based entirely on where the powder was in the case.

This problem reared it's head in some of the largest sporting rifle rounds ever shot with the advent of modern IMR type smokeless powders.
Many of the big double rifle rounds were originally for black powder and all of them quickly went to cordite when that became available.
Cordite was the perfect answer physically because of it's spaghetti like nature.
While not filling the entire volume, it did stay still occupying the entire length of the brass.
Some even had the necks formed after the cordite was inserted.
Cordite's downside was great temperature sensitivity.
Rifles started to blow after being sent to India and especially Africa.
The loads were reduced for tropical use.

Cordite eventually went away and I am not sure how much was ever available to handloaders.
Along comes the DuPont type powders we are familiar with.
They pack into a much smaller space for a given weight than cordite.
Double rifle reloaders quickly tried every filler imaginable and the factories (Eley and Kynoch) settled on a foam plug very like foam ear plugs.
They are still used in factory DR ammo and are available from Kynamco.
Their price precludes me from using them recreationally in target 44 ammo.

I settled on Grex shotshell buffer.
It's been out of print for quite awhile but Ballistic Products makes similar buffers.
The trick with these light powdered plastics is to make sure everything is under compression so the contents don't mix or move.
A typical load I'd make again because it's accurate:
44 Special, WW brass, WLP primer, 4.75 gr PB, 10 gr Grex, 240 SWC.
These chrono from 675 to 700 fps out of various 3" revolvers with low variance and excellent targets.
I think the filler also helps bump up or obturate the bullet by providing a quick spike in pressure as the plastic vaporizes.
It may help lubricate the bullet's ride as well (or the next one).
One of my best filled loads. Too bad PB is out of print now too.

Tip: Don't use any paper product for filler if you intend on using an indoor range.
You will leave an unholy mess on the floor in front of you.
Don't ask how I know this.

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__________________
NEMO
"Everything 44"