6.8 SPC (.277)
Aluminum is not full auto or bump fire rated.
Titanium can handle full auto or bump fire for a limited time/one magazine before cooling.
Stainless is full auto or bump fire rated but also for a limited time/two or three magazines before cooling.
These are conservative numbers and can vary based on load, barrel length, suppressor size and speed of magazine swaps.
As time progresses we will publish the limits we find. See FAQs for more information.