I should have noted that, Wayne - the 10% max. has always been suggested form the early 1970s to today, for the fast burning powders used in duplex loads - such as 5744 and 4759.

With the slower burners such as the noted '3031, more than 10% was needed to get good ignition and clean burning - as per the article - they worked well for me.

The largest ctg. I have ever loaded for, was the 30" .50 3 1/4" in a Shiloh Sharps, M74. I thought this was before I read about the use of IMR3031 in duplex loadings - but as I developed a smokeless load for that rifle with the 550gr. cast bullet using IMR3031 (1,775fps irrc)- with a case topped off with KAPOK from a old life preserver/flotation device, I'm probably remembering using 3031 in that rifle for duplex loading as well. Now that I think about it, I probably used 15.0gr. in the duplex load in that rifle as well as the .50 Alaskan.

I also recall that at that time (Shiloh .50 3 1/4"), I had some ICI 1F powder (still have 1/4 pound) that was exceptionally dense/heavy. I had read that Elmer Keith had said they should have named that case, the .50-170-700. Many laughed at him for this statement.
My 3 1/4" .50 Bell cases actually held 170gr. of that powder with a 550gr. cast RCBS bullet. Though dense, it was a poor quality powder of the late 70's, early 80's, the velocities it produced were lower than 140gr. 2f GOEX, also a not very good powder, back then - I do remember that ICI in 170gr. load sure kicked even though I had a nice wide Neidner butt plate on the rifle.