There is a very informative article concerning muzzle flash in the latest issue of the IDPA Tactical Journal (Vol. 5 Issue 2). The author, Charles Hamilton, did a pretty good subjective test of various powders available to handloaders. Unfortunately, he did not have the opportunity to use any Vihtavuori powders. Still, the results are interesting. His more "scientific" approach confirmed my casual observations, namely, that I will never again load with Power Pistol, and that AA#5 is a fairly good choice for tactical training loads.