DIFFERENT POWDERS PRODUCE DIFFERENT VIBRATIONS just like different loads do.
You might try a different bullet and the results might be opposite or even a different load, it is really difficult to reach any firm conclusions by shooting the same load with two different powders that have different burning speed and different potential energy.
If you really want a comparison then find the sweet point of each powder and compare using those loads. I normally use both the load and the bullet that shoots best to try and compare.