Burrard briefly mentioned Neoflak powder. It appears as if it was a dense powder of a slower burning rate than the then mostly used Bulks, such as Smokeless Diamond & EC or the dense Ballistite. This would have allowed the heavier shot load without increasing the "Maximum" pressure. The faster burning powders could only be kept within the 3-ton limit by using reduced charges as in the low-velocity principal.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra