I think he's trying to tell you that it is a inappropriate choice, not that somebody somewhere has used it and lived to tell about it.
Generally speaking, Blue Dot is considered a suitable choice for some handguns. I have been around a long time and have never heard of somebody loading a 308 with Blue Dot unless, (perhaps) when fireforming cases for use in a wildcat.
So, in the first place, most people understand that the place to start is with published data. In this case, you decided to work up a load with no data whatsoever. I am not surprised that you had difficulty in locating application data for 308 using Blue Dot, and further noting that the bullet used, has not been identified.
Two years is a relatively short history, as far as handloading experience. You should probably be careful using fast burning powder in a large case with no data, but the question I have is why? Is it because you use Blue Dot in your S&W500, or maybe because you happen to have it on hand? BB