Powder Burn in Chamber or Bore?

Smokeless powder doesn't really "burn." It is made up of one or two unstable chemical compounds, nitrocellulose and nitroglycerine, that decompose by deflagration with release of heat and gas when initiated. I'm not trying to be a jerk, Jim, but I don't think your definition of deflagration matches those the rest of us use. What you are describing would be more appropriately called 'detonation'. However, smokeless powders are designed to deflagrate. Detonation in a firearm usually results in unintended high speed disassembly (catastrophic failure).

Wikipedia:
"Deflagration [1] (Lat: de + flagrare, "to burn down") is a term describing subsonic combustion propagating through heat transfer; hot burning material heats the next layer of cold material and ignites it. Most "fire" found in daily life, from flames to explosions, is deflagration. Deflagration is different from detonation, which is supersonic and propagates through shock." [emphasis mine]

Farlex dictionary:
"def·la·grate:
To burn or cause to burn with great heat and intense light."
"deflagration - combustion that propagates through a gas or along the surface of an explosive at a rapid rate driven by the transfer of heat"

Merriam-Webster:
"deflagrate:
to burn rapidly with intense heat and sparks being given off"

Compare that to "detonate":
Merriam-Webster:
"detonate:
to explode with sudden violence"

Wikipedia:
Detonation involves a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations are observed in both conventional solid and liquid explosives,[1] as well as in reactive gases.
...
In terms of external damage, it is important to distinguish between detonations and deflagrations where the exothermic wave is subsonic and maximum pressures are at most a quarter of those generated by the former. Processes involved in the transition between deflagration and detonation are covered thoroughly for gasses by Nettleton.
...
Unintentional detonation when deflagration is desired is a problem in some devices. In internal combustion engines it is called engine knocking and causes loss of power and excessive heating of certain components. In firearms, it may cause catastrophic and possibly lethal failure." [emphasis mine]

The fact that burn rates can be controlled by granule size, shape, and density, should be a big hint that it's deflagration, not detonation.

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