Any reasons for the conservative numbers from sierra?
Unfortunately there are many stories and threads about your exact points.
Sometimes this difference is significant, and sometimes it is in the noise. The context determines the difference in that level.
When we commission pressure test barrels, they are generally pretty well made and reliable. Even with the best and most careful work, there is dispersion in the results.
Some of the dispersion is the pressure measurement system, some is just the nature of internal ballistics and includes the components of the recipe.
Barrels, bullets, brass, primers, powder batches, can all create differences. There can be a significant bias in results just due to brass in some cartridges.
At the end of the day, how those values are reported out can vary between organizations (lawyers...) . One organization might report only the average while a different one may put a statistical safety margin on their output. There have even been some publications that were base solely on software simulations.
Some reamers and bullets can create big differences due to things like freebore or the design of the lands/grooves.
So, in terms of differences in publications, some of the reason is the real dispersion and calibration error of the work, and some of it is due to differences in the philosophy of the different test facilities. One outfit may elect to run only specific pressure test barrels with barrel and chamber specs that differ from place to place, while additional reasons can include some places testing with samples of actual rifles.
I'm tired and will cut this short, but there could be a long discussion on how many different reasons there are for the real differences as well as the political ones.
Try not to get too worked up about the differences, but that is not to say it isn't good to get as much research done as you can from as many different sources as you can manage to find. The thing to do, is develop your own background and track your results compared to those publications to know how to stay out of trouble. Good Luck, YMMV
