The 1966 Herters reload guide has some shotgun loads listed and although they say it has uses in pistol loads they don't give any that I can see. Here is what they say about their powders (lots of marketing verbiage) ....
"A new series of shotgun powders developed by Herters for the Handloader as well as factory loading. Although primarily designed for loading shotshells these versitile powders have also given excellent results in many pistol and revolver cartridges.
Herters shotgun powders are available in four ballistic levels denoted by the numbers 160,162,164 and 169. The speed of burning of these powders decreases as the numbers increase. Herters 160 is the fastest burning and 169 is the slowest.
Herters shotgun powders have excellent free-flow properties and are well suited for use in automatic loading tools. Granules in Herters shotgun powders are sufficiently small to free-flow and yet they cannot enter the flashhole of the primer and impair ignition.
Color Coding is used to easily identify the four powders. Granuals are in the form of grayish-green discs. 162 contains yellow granules, 164 contains white granules while 160 and 169 have no colored granules. These powders are pourous and are therefore easily ignited by the primer, furthermore the desired ballistic level is achieved by adjusting the degree of porosity rather than applying a coating, which generally tends to impair the ignitability of the powder.
Herters 160- Designed for the handloader as well as factory loading. 160 is the fastest burning of the three Herters shotgun powders. This is a pourous powder and easily ignited. It is intended for light loads such as 1 ounce shot charge in 12 gauge and 7/8 ounce shot charge in 16 gauge. It has excellent free-flow properties and is well suited for use in automatic loaders.
Herters 162- Similar to 160 this powder is somewhat slower burning and well suited for 12 gauge with 1 1/8 ounce shot charge. It can be used in any gauge shotshell except 410. As is true with all Herters powders it is virtually unsffected by wide temperature and atmospheric changes and is suitable in all climate conditions when using paper cases. A small portion of the granuals are yellow in color for easy identification.
Herters 164-This is a slow burning shotgun powder. It is designed especially for use in heavy and magnum loads in all gauges. It has white colored granuals which identify it from the other powders. Granuals are greyish-green disc-shaped measuring 0.017 inch in diameter and are .013 inch thick, as are the other Herters powders.
Herters 169- Designed for 3 inch Magnum loads 169 is suitable for use with 1 7/8 ounce shot loads. The granules are grayish disc-shaped with no color granules and are of the same appearance as the other Herters powders. A slow progressive burning powder."
In the load section its a bit difficult to make heads or tails of what is like what but I see 162 loads often listed next to pb, hi-skor, herco, 5066 and unique but the charge is not the same.
Maybe this will give you some clues on tracking it down. good luck.