I've done mine and others with a mix of glass beads and black beauty, 2/3 to 1/3 respectively. It is coarse enough to get rid of the machining marks and cut through the hardening on the edges of laser cut sideplates but produces a great finish that is evenly colored.
Straight black beauty might be too agressive so if you go that route, watch the edges, serial numbers/markings and anything threaded...it cuts fast and deep.
A forum community dedicated to Browning 1919 A4 firearm owners and enthusiasts. Come join the discussion about performance, gunsmithing, restoration, troubleshooting, reviews, accessories, classifieds, and more!