[mrerick]

Some powder occupies more volume by weight than other milled shapes.

Titegroup is known for being compact. The downside is that it's easier to double or overcharge a case with a compact powder.

Would a "full" cartridge case become oxygen starved? Unlikely. There is a fair amount of oxygen bound up within the powder granules themselves (in addition to carbon, hydrogen) of nitrocellulose. There is also oxygen between the grains of powder, which never sit solidly against each other. The surface of powder is also porous.

https://en.wikipedia.org/wiki/Smokeless_powder

There is some interesting discussion about the way powder within a cartridge case burns. Taken to extremes, it becomes more important in artillery and canon design.