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It's not volume dependent. It's technology dependent.
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It's both.
I've built 9mm cans the size of rimfire stuff, and giants on the other end of the spectrum, as well as recoring some monstrosities that made modern .338 Lapua cans look, well...... "athletic".
You can only do so much with inadequate volumes regardless of design efficiency, but big volume certainly won't make up for crap internals. There's always a balance. Where that balance lies is largely host dependent, though, both in terms of backpressure on autoloading hosts as well as the point of diminishing returns with size & weight.
On that note, however, IME, conventional core designs in oversized cans do not work well. You can't just scale up a solid 1.375x7" pistol can design to 2x10" and get good results with the same round. Seen so many Form 1 cans where "bigger is better" was the precept with disappointing results. The additional volume can absolutely be utilized effectively, but it has to be done a certain way or you'll end up with something that actually performs worse. Coaxial is really the name of the game with the big things, but figuring out exactly where and how much to bleed off into the coaxial chamber(s) for optimal efficacy, as well as the core size to use within, depends on the main tube size and the host firearm.