I have several comments on this. First, your problem could be that you are holding the torch too close to the metal. The hottest part of the flame will be just beyond the blue cone, and this will also be the reducing part of the flame, which will probably be better for melting this copper alloy.
Since the melting point of brass is about 1650 to 1720F and a propane/air flame is at least 1900F and MAPP gas is hotter than propane, your setup might work with propane. I see by Google that MAPP gas requires a “Turbotorch” head, so it could be that the mix of fuel and oxygen is just wrong with the propane head you have. If backing off to a different part of the flame does not work, you could try using a propane canister (about $5) and see if using this torch head with the fuel it is designed for works. Using some kind of cove around the crucible, as Rob describes, may help. You could also look for a MAPP gas head and use it with the MAPP canister you have. I see some heads on line for about $15.
I did see a video where someone melted brass to cast a half dollar sized piece about twice as thick as a half dollar…he used a propane torch with a little larger head than yours to melt in a crucible and it took 6 minutes, 30 seconds. So you may need to be persistent. I’m surprised Rob’s torch wouldn’t melt brass, but maybe it just takes a while. Certainly propane/oxy would do it, but getting a new torch and two regulators in addition to an oxygen canister is going to run into much more money and IDK whether you have other contemplated uses later that would make this a good purchase. -royjohn