...Also note from earlier in the discussion that the energy density (kJ/kg) is greater for PP. This comes from it being a double-base powder with both nitrocellulose and nitroglycerin in it. Nitrocellulose has a negative oxygen balance when it burns. That is, the amount of carbon, hydrogen, and nitrogen released from it that could be oxidized is about 24% greater for cellulose hexanitrate (the main nitration of the cellulose) than the amount of oxygen released can oxidize. This is why there is carbon left in the bore. Nitroglycerin, on the other hand, has about a 3½% oxygen surplus when it burns. Thus, not only does it oxidize completely, it provides a little extra oxygen that reduces the nitrocellulose oxygen deficit a little. The net result is more oxidized gas molecules (CO, CO₂, H₂O, NO, NO₂, HNO) are produced per grain of the double-base powder than you get with a single-base powder.
tangolima said:
I think manufacturers are willing to spend money on analyzing competitor's product, if that's their competition and accurate info is not readily available. Mostly it is available. Bought a license of QL and you have it.
I'm sorry I missed this post when the thread was still new. Actually, I got it directly from Hodgdon a while back that they do not test competitor's products. I was looking for data on a powder not listed in QL at the time (Hodgdon and others) and asked if they had it. I was told it costs something like 30-50 k$ to have a lab fully characterize a powder, so they would have to spend millions to get all their competitor's powders analyzed. And then, what would they do with the information? They order powder made to a formulation rather than to all those modeling characteristics, which would be hard to control independently. A finished lot of powder then has only its burn rate tested. The new lot is then milled (blended) with held-back past lots of the same powder formulation that came out of the factory either faster or slower, whichever is needed, to bring the relative burn rate of the new lot in line with their reference powder's performance, plus of minus 3%. I assume this test is for relative burn rate rather than the PET-initiated water tank test of burn rate that determines Ba. The relative burn rate test is simple and more meaningful when you are comparing it to past lots of the same formulation rather than comparing different formulations whose different characteristic burning curves will affect outcomes. This relative burn rate test just involves loading the same charge into the same cartridge component combination and blending to match the peak pressure results with what the reference lot produces. Not too complicated.
For the modeling numbers, QL's author, Hartmut Broemel, uses a clever workaround. He owns the lab equipment to do his own vivacity bomb test, then uses the output of that single test to deduce the other powder characteristics. This deduction function is built into the program, just in case you are able to get your own vivacity bomb testing done. You click on the powder editing button. In the lower-left corner of the window, click on the bottom button to choose to edit bomb output, and you get a table that lets you put in the vivacity bomb time and pressure numbers. The software then generates the full list of characteristics from that information. So, the powder characteristic tables in the program are not lab-determined independently tested characteristics but rather are "behaves-as-if" numbers deduced from that one test. This is kind of the heart of Herr Broemel's invention of the software, this clever lab shortcut. How exactly it compares to independently determined characteristics depends on several things, but it gets reasonably close. You can tell because some of the powder makers on the other side of the pond publish some of the characteristics they've measured for their own production (these are actual powder makers, not distributors like Hodgdon). Vihtavuori and Somchem, for example, will give you some numbers, like energy content, and you can compare them to what's listed in QL. They don't match exactly because the factory publishes target numbers, and Herr Broemel's measurements are of lots purchased off the shelf and tested. He has no way of knowing exactly how close to average a particular test lot is, so his numbers will shift some from the makers' target numbers because their lots shift some from their target values.
If you read the QL manual completely, a lot of that information is in it.