Well, technically black powder doesn't detonate in a gun. It deflagrates. I understand it can be detonated, but that it takes a very large quantity (tons) and requires high nitro dynamite as the initiator to make it happen. What's mainly different about black powder from smokeless is the ignition speed is fairly constant because it is pre-compressed when it is caked before corning, and then as each grain burns inward it does so at a constant rate and the surface area gets smaller and smaller meaning the amount of gas evolved per microsecond get smaller and smaller. That's the definition of digressive burning. The fact the grains burn at a fairly constant rate means larger grains take longer to finish burning inward, but they never evolve gas other than digressively in inverse proportion to their grain surface area.
Progressive powders make gas at an increasing rate per microsecond up to the point they reach their progressive burning limit (z1 on a vivacity plot). Stick powders do this by having a deterrent coating that stops the outside from lighting quickly, but has perforations that light fast and burn from the inside outward, causing the burning surface area to grow rather than shrink as it burns, so the rate of gas evolution keeps getting faster (the definition of progressive burning) until the expanding burning surfaces burn through to each other and to the underside of the outside deterrent coating and the core in the center of the perforation array is burning inward with diminishing surface area, at which point it has flipped over to digressive burning that wraps up the burn.
Spherical smokeless propellants are made to burn progressively despite the fact their burning surface areas are shrinking as their grains burn. This is done by soaking deterrent into the grains in an exponentially diminishing concentration. That makes the grains burn very slowly when their surface areas are still large, and then as they burn inward, the rate of combustion increases more rapidly than the burning surface area diminishes so that it more than compensates for the loss of burning area up until the deterrent gradient has been burned up. Then for the last little bit of burn, it goes over to being digressive as it finishes off its core.