Re: powder loads going down??
There's actually a couple of reasons for this. One (not surprisingly) is fear of litigation. In the early days of reloading manuals, there was some pretty scary stuff out there. Not all manuals were done with pressure testing equipment, and many were done with the same tools and tecniques available to the average handloader; micrometers and the obvious appearance of pressure signs. Today, most (but not all) pressure test their loads from start to finish, and actually adhere to SAAMI or CIP limitations in re pressure. This is not to say that the loads have been "lawyered back" as much as they have been forced to keep their data within a more narrowly defined range.
Unfortunately, I often hear or read the advice that modern maximum loads aren't really "max", and that there's a safety factor incorporated in the data. I want to be absolutely clear on this; that's total BS, at least with the firms I'm familar with. The max load listed was the max load that the range/lab determined, as is. There were no safety factors "added" to this mix, and anything beyond that merely relies on the strength of the actions to deal with what may amount to proof loads.
Another is the advancement in pressure testing equipment. In the past, pressure testing was normally done via the copper crusher method, resutling in the CUP values you'll see listed in many older manuals. Putting it bluntly, it was determined that copper crushers don't normally reveal true peak pressures. Upon firing, pressure can spike fast enough, and begin to drop again while the metal of the copper pellet is still deforming. In short, the pressure spike was faster than the pellet's abiity to measure and record it. This simple fact gives erroneously and aritifically low pressure readings, making the load appear safer than it actually is. The move to conformal transducers and piezo electric measuring equipment opened a whole new world, and allowed a much better understanding of these spikes. Again, some scary stuff was revealed. Today, this is the most common method of pressure measurment, and it's vastly better than the old CUP values. The result of this, however, is a gradual trending downward in maximum reccomended loads, as you're seeing.
The bottom line in all this, is that you want to use the latest data available, from the most current sources. If you have two or more manuals available to you from the same maker, use the newest version. Where differences between manuals appear, both of whom may be using the same pressure measuring methods, you're likely seeing the results of the effect of the difference in various components. That is, different primers, cases and bullets (even of the same weight), or even differences between lots of the "same" powder, primer etc..
In my library, I have a complete set of loading manuls from virtually all manufacturers, going back over thirty years. While there's intersting and good information in all of them, I use data from only the newest. Some of the older ones were downright scary. P.O. Ackley's manuals are a great example. Lots of wisdom and some very good information contained therein, but many of his starting loads are at (or even beyond) what we now recommend as maximum loads. Some would blow primers or badly expand primer pockets after a firing or two. Just a little something to think about.
Last edited by Kevin Thomas; 03-29-2011 at 10:05 AM..