I’m reading the small 1951 book, “Major Ned H. Roberts And The Schuetzen Rifle”. On page 30 and 31 the use of what today might be called a duplex load is addressed. 

A small amount of BP called “a BP priming load” is first inserted and then the rest of the case filled with what was probably at the time a smokeless powder.

Is/was this called a duplex load? Is this practice used today by any of our Schuetzen match shooters? If so, what are the two powder's most frequently used?

Seems a bit intriguing. 

Tom

I believe that today a duplex load refers to a black powder load, I.e. a few grain (like 3 of 4227) and then your black powder load on top. Supposedly the smokeless helps ignite all of the black powder, more efficient. True or not I won’t state but I do use it and the barrel definitely stays cleaner from shot to shot.

Oakdale
At the recent ISSA Schuetzenfest at the NRA Whittington Center near Raton, New Mex. we held our 1st annual black powder bench rest match. It was 50 shots at 200 yards using the German ring target. Black powder, duplex and black powder substitutes were allowed. As a participant, I had intended to shoot duplex but due to several issues I ended up shooting straight black powder. But I digress . . .
Over the past years I have shot a quite a bunch of duplex loads in .32-40, .38-55 and .38-50. The priming smokeless I have used the most and have had the best accuracy with are 4759 and 4227. I've used between 3.5gr and 5.0gr depending on the cartridge. I all cases, the remainder of the case was filled with black powder, trickled into the case through a 24" drop tube with a card wad pressed onto the case mouth to hold everything in place. I have shot duplex with both breech seated and muzzle loaded with equal accuracy. Depending on the temperature and humidity, sometimes muzzle loading can be shot dirty (no bore wiping between shots) with good accuracy.
If you have seen my book The Golden Age of the American Schuetzenfest, I go into some detail about loads and results with different calibers and rifles.

In my .25-25 Stevens Ballard, I only use black due to it''s cast action. I tried duplexing..PB left bore looking like a smokeless load was fired., tried IMR 4227 & 4759.  Still required 1 barely damp patch thru for match accuracy...same accuracy for straight Swiss 3fg...so I thought why bother.