What type of headspace does the M249 automatic rifle have?

The M249 automatic rifle has a fixed headspace, which means that the dimensions of the chamber and bolt are set at the factory and do not change during normal operation. This is important for ensuring consistent performance and reliability of the firearm. A fixed headspace helps maintain proper alignment of the cartridge within the chamber, which in turn ensures reliable feeding, firing, and extraction of cartridges.

In contrast, adjustable headspace would allow for modifications to be made to accommodate wear or variations in ammunition, which is not typically the case with the M249. Variable headspace suggests that the chamber can accommodate different types of ammunition, which does not apply to the M249’s design. Detachable headspace could imply an interchangeable part that allows for adjustment; however, this does not align with the established construction of the M249. Thus, a fixed headspace is fundamental to the design features and operational functionality of the M249 automatic rifle.