Several items need to be cleared up here. First, powder manufacturers test and blend cannister powders for a nominal burning rate as under standard conditions. The test sample is a standard quantity sample that is burned in a caloric bomb held at a standard test pressure during the burn, and gives a result in liters of powder burned per second. The rate is not tested at any other pressure. All the other powder characteristics you see listed in QuickLOAD's data, plus the case volume information and bullet and bore cross-sectional area information, are needed tell QuickLOAD's calculator how to adjust the burn at other pressures. The concern by powder manufacturers is that established loads of their powders not raise pressure excessively. That varies with more than just burn rate, but burn rate seems to be the best general predictor. It doesn't predict pressure well-enough for certain extremes, like overbore chamberings or exceptionally small cartridges.
An example of that last point is that Hodgdon's Extreme series of powders made by ADI to have good burning rate immunity to temperature change. Varget in the .308 does exactly that, showing remarkable consistency under temperature variations. Many shooters also use Varget in .223, but have observed Varget's temperature immunity doesn't seem to hold up in the .223. Apparently the little bullets just get out too quickly for the pressure/temperature stabilizing relationships designed into the powder to still apply well. So, the rules for pressure in the littler chambering will be a bit different, especially at temperature extremes. I would not be surprised to see it prove more sensitive to lot variation, too, for that reason. I would not be surprised if something blended to withing 3% in the standard burning rate test was out 10% at some other temperature and pressure condition. Indeed, you can probably bet it will be.
BTW, obviously, the burn rate standardizing blending is not done for non-cannister grade powders, like H110 aka 296. For that matter, with IMR made in Canada, Hodgon Extreme powders made in Australia, Vihtavuori in Finland, and still others packing powders from plants in other countries, I have no idea what percentage of powders sold in this country observe the SAAMI burn rate blending standard even where it does apply to your results?
The main point I am trying to get to is that burning rate order for powders can change when they are not at the one standard test pressure or in the standard chamberings they are expected to be used in. This occasionally results in a powder you think should be better in a particular application not actually proving to be so. It also results in more lot-to-lot and condition dependent pressure variation in some chamberings than in others. From a safety standpoint, the bottom line, as always, is to back down to starting loads and work up when changing powder lots.
Also keep in mind that while burning rate is the most significant ranking characteristic, the progressivity and energy density and all the other characteristics can vary lot-to-lot, too. VihtaVuori Oy's 2nd edition manual, figure 2.8 is an interesting chart of different burning characteristics for different grain shapes. Additives and surface treatments alter that, too. I don't know if their current manual still has it, but the whole first portion of the 2nd edition was a pretty good education in powder basics. It is eye-opening, too, to see just how differently powders can burn.
It's not clear to me how much the manufacturers test the non-burn rate characteristics? I once tried, when QuickLOAD was new and had a smaller database, to get that information directly from Hodgdon for a Hodgdon powder that was not then the database. I was told, a bit gruffly and defensively, that such information was "proprietary", and that, besides, it costs about $50K to have a lab run all those tests, so they don't do if for all their powders. Of course, Hodgdon doesn't make their own powder. I know VihtaVuori keeps a full calorimetry lab (a photo is in the manual), and perhaps ADI does, too? The Hodgdon tech I was speaking to was astonished when I told him QuickLOAD already had characteristics for most of their powders, and he seemed irritated and taken aback that someone had got this "proprietary" information and wanted to know how that was possible? I pointed out all they needed was a calorimetry lab. I tried to explain to him, having several patents myself, I had been thoroughly familiarized with the legal aspects of intellectual property rights, and that proprietary information had no legal standing other than you could sue someone for violating a contractual agreement not to reveal it. It isn't like a copyright or a patent or a registered trademark, but is strictly dependent on the company's ability to keep something secret. That, in turn, is only as good as your ability to ensure someone examining the finished product can't deduce the proprietary elements. A secret process can be kept proprietary only if the finished product contains inadequate clues as to how it was made. But if you think you can keep the size of the gears in a transmission secret, you can forget it because people have measuring tools and can take things apart. You keep rights to measurable things by patenting them, and rights to invisible things by keeping them secret. Coca Cola and Heinz Ketchup have been kept their formulations and processes secret for many decades because they can't be simply measured after eerything is combined, mixed up and cooked up, and, unlike a patent, successfully kept secrets don't become public domain after 20 years.
I'm drifting a bit afield, here. QuickLOAD's author, Hartmut Broemel, has his own calorimetry laboratory. He personally has to pay for the powder and find the time it takes to run the standard tests on his samples. The data, therefore, is mostly taken from a single lot. The most recent powder database has a couple of changes over the version currently on sale (he gave me a beta version when I found a bug for him), so he does get to retesting with new samples occasionally, but in the main you cannot know how typicial any one of the database samples he measured was? You can see the difference in the ADI results above. Run some others you know are actually the same powder, like H110 and 296. You'll get a 10% peak pressure difference for a given load because that's how different the two samples were when Mr. Broemel measured them. It gives you a sense of the variation.
A couple of points on using the program that I've learned over time:
First, be sure to replace the default case water capacity in the chambering selected with the actual case water capacity measured in the brand of case you use and fireformed in your gun's chamber. Peak pressure depends on the volume the powder is burning in and that will be affected by the volume your gun's chamber lets the case expand to. This can make a good bit of difference in the results. I've seen over 80 fps muzzle velocity change, to give you a sense of it. If you are unsure how to make the case capacity measurement, go to my file drop site. I have an Excel file with instructions and calculators for making the water capacity measurement posted there. I have tested the Excel file in Open Office's spreadsheet program, Calc, to make sure it works there, too. If you don't have Excel, the Open Office Suite may be downloaded free from
openoffice.org. My public file repository is at
drop.io/Unclenick.
Second, use the bore cross-sectional area calculator. This is less important than case capacity. It typically makes only a few feet per second difference but is affecting bore friction.
Third, QuickLOAD's background information suggests you add 7% to straight wall case capacity to get more accurate predictions from the calculators, which were actually developed around bottleneck rifle cartridges. I find this is reasonable for the 30,000 psi and up cartridges, but that for the older lower pressure cartridges it is not usually necessary.
QuickLOAD does not work well with lever guns shooting high pressure loads, like the .307 Winchester. The lever actions stretch too much, having their locking lugs way at the back of the bolt. QuickLOAD will predict higher pressures and velocities than these guns see because their cases stretch so much that they kick the lever slightly and you can't completely close the lever on them again. 2 to 4 grains extra water capacity is not an unusual change due to that stretching in these guns.
I have noticed a number of the bullets in the QuickLOAD database have had their dimensions taken from photos or drawings that may have been slightly stretched on one axis or the other where they were published. If you have a particular bullet you use a lot, measure it carefully and enter it into the database. For example, over time I found two distinct sets of dimensions for the Sierra 175 grain .308 MatchKing bullet, which I use frequently. I wound up altering the database to give it correct dimensions as I had measured them on an optical comparator. You can edit the databases in Notepad if you want to correct them without making a new entry. However, if you want to carry over your corrections to new version installations, you are better off to make a whole new bullet company file under your name so you can save it in a backup disk and import it to any the new or upgrade installation all at once.
Finally, if you have a chronometer with good absolute accuracy, like the old Oehler 35 or the CED Millennium with the IR sky screen option, or the PVM-21, then you can use readings from it to make slight adjustments to the powder
burning rate factor to tweak the powder performance to match your lot, then save it under it name and lot number. Chris Long has a paper on adjusting to correct for actual performance by tweaking both the burn rate and the bullet weight by not more than a grain to get exact correspondence. I prefer to tweak the burning rate and the bore cross-section area where it works, but you can experiment on your own. Long's paper can be
found here.
When you start QuickLOAD a disclaimer comes up. There is a
Page Down button that takes you to a very basic explanation of the program operating principles. I recommend you read both as both contain some information that will help you understand what the program can and cannot do.
