Nice thorough research CP! I am one of those that agree with you and the powder manufacturers. The coating on the powder is called "deterrent coating" and there are several chemicals used, one is composed of a chemical called DNT (Dinitrotoluene). They are applied to the kernels of powder in varying degrees to control the burning characteristics of the finished product. Tumbling removes this coating and can boost chamber pressures to beyond safe limits. Removal of case lube should be done after resizing and before priming if tumbling is desired.
Note: Case lube should ALWAYS be removed from case exteriors because residual lube can "raise pressures and bolt thrust to potentially dangerous levels. " (Sierra Rifle Reloading Manual - 4th Edition)
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