I've been watching this thread since it started and held off making any comments until I could see where it was going.
Back in the mid-60s, I worked as a lab tech in a firearms lab that was affiliated with the Dept of Justice. We tested every current production firearm and every current production type of factory ammunition in both handguns and rifles. The task was to develop a data base that could be used by investigators to determine crime scene information, much like the CSI of today. It took a crew of engineers and technicians two years to complete the task. At the end of testing, all team members concluded the information was nearly worthless.
We found the same lot of ammo fired from different guns gave dramatically different results. Likewise, the using the same gun with different ammo gave different results. There were just too many variables for conclusive results.
A good example was temperature, not the ambient temperature but the temperature of the rifle's chamber. Though safe in a cold chamber, that same load could go off the charts when the chamber got hot. Another interesting pressure problem dealt with muzzle position. When powder didn't fill the case enough, the gun became "position sensitive". We found as the powder laid in the case, the surface exposed to the primer had more to do with pressure than the actual grain weight. There are dozens of other variables such as different brands of powder and different lots within that same brand, bullet seating depth, bullet design, cases (sometimes different even with the same headstamp), and primers. Then couple those variables with chamber, throat, bore dimensions, barrel length and other gun parameters and you get a near infinite set of combinations. Keep in mind, this was factory ammo where the manufacturers had way more testing capability than any reloader today.
It's no wonder bullet and powder manufacturers want to keep the pressures under control. It's bad for their business if someone should blow up a gun based on their loading data. I could just imagine the cumulative effect if you just happened to stumble on the wrong combination.
I started reloading when I worked for DOJ and have been doing it every since (40 years). I take a scientific approach by first finding the powder that best meets my needs, then using established data to work up loads. The biggest single mistake most reloaders make is trying to use one or two powders for all their loading applications. There's a reason why powder companies make so many powders with different burn rates. Likely, one will be superior with accuracy and velocity while keeping the chamber pressure below dangerous levels. That same powder might not be worth a hoot in another cartridge or even a different bullet. The second mistake is pushing the envelope. As others have stated; if your gun isn't powerful enough, buy a bigger one. There's nothing wrong with trying to achieve best performance but don't try to get 22-250 velocities out of a 223.
I hope this thread continues with good advice from others. These are not "rules" we are dealing with, they are good common sense precautions. Yes, I've been known to go over the limit a few times but the will to live brought me back on track. I hope others make the same decision before they experience a kaboom.
