[Slamfire]

How you want to call it, cartridge headspace is critical for function and safety.

Cartridge cases cannot expand forever without rupturing somewhere on the side wall. That is why the difference between Go and No Go is typically 006”. Cartridge stretch above that and there is a real risk of case head separation, depending on brass hardness.

Lee Enfields stretch so much that cases fired in those things develop case head separations in a couple of reloads.

You don’t want an interference fit because when the barrel and lugs relax, they will be in yield during combustion, the interference fit in the chamber will be even more, causing hard extraction or a failure to extract.

This is why hot loads cause sticky extraction. Pressures expand the case, barrel and lugs, and once the pressure is removed, there is an interference fit.

Excessive headspace can cause lug/receiver seat peening. I understand this is more of an issue with machine guns, they fire a lot more rounds, but still, the further the case head is from the bolt face, the faster it will be moving when it impacts the bolt face.