Don't take my word for it, take IMR's
https://imrpowder.com/wp-content/upl...-loads-r_p.pdf
The PDF is a small data sheet, but the paragraph above the data sheet explains the load, 70% starting, etc.
They must have given you to a salesman. Universally across the board, salesmen usually give out bogus info.
I am still in the development stage for working up a trailboss load for my 470. It will not regulate with factory jwords in its regulating load weight, using trailboss. I'm in the process of trying to track down some cast boolits for it and possibly experiment with lighter weight projectiles.