I have never worried about a double charge.
Clays is the bulkiest powder I can remember using for 40, lots of guys think there is a really good chance of blowing the gun up with major loads though.
Blue Dot is bulky, and will easily make major. Haven't tried to double charge one but I don't think you can do it without a spill.
I use the same TG load you use now and am looking for a new load. I don't like the heat it puts in the gun, on the rare occaision that I actually get to do a little live fire practice the gun gets hotter faster with TG than anything I have ever used. I have to pace my practice at a much slower rate than I would like. My 'problem' is that TG is cheap, meters essentially perfectly, is VERY accurate, and I have it on hand.