You can take a sharpie marker and color the edje....just the secondary bevel....the final grind. Then go to the steepest angle you have (maybe 30deg?) and take a few light passes. Inspect the edge and see how the marker is grinding off. That will give you an idea of what angle to proceed at.
Most BM's in my collection are ground between 30 and 40 degrees, and rarely are they the same on both sides. Usually they're off a degree or three from one edge to the next. Depending on the blade shape, primary grind, and intended use of the knife, I lean toward more shallow angles (less obtuse). When the knife reaches the point where it needs its first "real" sharpening, I'll usually regrind both edges to a uniform and steeper grind, sometimes aiming for about 25 degrees (12.5 or so per side).
