Don't take this as flippant as it sounds but just fill the case with trailboss and put the bullet on top. :mrgreen:
Only half kidding. Just don't compact the powder at all. Leave enough room to seat the bullet. Do this and weigh the resultant charge and I am willing to bet you will find it within the bookends of the company listed loads.
Trailboss is a great mild load powder. I have not found it to be the best for accuracy but that is not what it was developed for either.