Lost Sheep's comment: 3/10ths grain spread for an average charge weight of 45.3 grains of IMR4895. A lot of info on powder measures accuracy and use is on the 6mmbr web site;
www.6mmbr.com.
Thanks for the link. I will have to read that later (I am at work taking time during my lunch break right now).
Your reference to a powder's pressure/temperature band is the first time I've ever heard of such a thing. I don't think any powder company list it in their load data, do they? I don't think its something that most people know about, use, nor understand or even heard of; it ain't axiomatic to me.
I apologize if I came across as snarky. The idea that powder works best within a particular pressure/temperature range came to me from various discussions of performance and my observation of how quickly powder burns at 14.7 psi vs 14,000 psi and higher.
I have personally observed that smokeless powder burns rather slowly at normal atmospheric pressure (around 14.7 psi), but much more quickly (inside a cartridge, for instance) at higher pressures. I understand also that the release of the oxygen tied up in the nitrates in the propellant is faster at higher temperature and pressure than at lower temperature and pressure, contributing to a quicker burn. Also, anecdotes of incomplete combustion of propellants when charges are reduced implies that pressure has something to do with performance, that performance at low pressure can be erratic.
All this leads me to the belief that (like many other chemical reactions) the speed of the reaction depends on environmental factors inside the cartridge. Pressure and temperature are the most obvious to me.
Essentially, the same idea that requires a narrow range of fuel to air ratio in an internal combustion engine before you get efficient power.
So, to reference your penchant for providing links, provide one that clearly explains a powder's pressure/temperature band as well as a table listing powders' numbers for that. I'd like to know what it's all about.
Sorry, I don't have one. If I find one or more, I will post. What I posted above is all I have right now except for a post (I think it was from UncleNick) who referenced the speed of oxygen release being dependent on temperature. But I did not save a link. Sorry about that.
I have never seen a table such as you describe. I expect that may be because the powder makers know that most loaders do not have the equipment or knowledge to make use of that raw data (the temperature probe you mention, for instance).
And also a link to some place where reloaders can buy a temperature probe to measure their powder burn temperature to ensure it's within specs. Reloaders can buy piezo strain gauge systems to measure their loads' pressures.
As I said before, I did not mean to criticize your post, only to ask you to provide some direction to those who want to research further. You are obviously expert in the practical matters of shooting accurately and loading quality ammo, and I respect that. The theoretical aspects of the shooting sports (internal ballistics, mostly) is a bit more esoteric than most of us want to pursue, but any boost from your knowledge base in that regard would be helpful to some who want to do that.
Lost Sheep