The M16A1 was the finalized production model and was produced from February 1967 until 1982. To address issues with the XM16E1, for the M16A1 a closed, birdcage symmetric flash suppressor with open side slots to the top, bottom, left and right replaced the XM16E1's three-pronged flash suppressor, which caught on twigs and leaves, from 1967 onwards. Various other changes were made after numerous problems in the field. Cleaning kits were developed and issued, while barrels with chrome-plated chambers and later fully lined bores were introduced. A small storage compartment inside the stock was introduced. The buttstock storage compartment is often used for storing a basic cleaning kit. To promote reliability and durability, the mechanical behavior of the operating system was revised to make it compatible for using US military issued ammunition loaded with WC846 ball powder (which reaches peak pressure significantly quicker than the extruded IMR8208M powder and increases the cyclic rate of fire for which the operating system was originally designed). Revisions like reducing the diameter of the gas port to mitigate the higher port pressure caused by the ball powder to properly gas the operating system again, updating the buffer assembly, changing the bolt carrier surface finish to manganese phosphate and the gas tube material to stainless steel contributed to improved mechanical behavior.
The M16A1 was the finalized production model and was produced from February 1967 until 1982. To address issues with the XM16E1, for the M16A1 a closed, birdcage symmetric flash suppressor with open side slots to the top, bottom, left and right replaced the XM16E1's three-pronged flash suppressor, which caught on twigs and leaves, from 1967 onwards. Various other changes were made after numerous problems in the field. Cleaning kits were developed and issued, while barrels with chrome-plated chambers and later fully lined bores were introdu.ced. A small storage compartment inside the stock was introduced. The buttstock storage compartment is often used for storing a basic cleaning kit. To promote reliability and durability, the mechanical behavior of the operating system was revised to make it compatible for using US military issued ammunition loaded with WC846 ball powder (which reaches peak pressure significantly quicker than the extruded IMR8208M powder and increases the cyclic rate of fire for which the operating system was originally designed). Revisions like reducing the diameter of the gas port to mitigate the higher port pressure caused by the ball powder to properly gas the operating system again, updating the buffer assembly, changing the bolt carrier surface finish to manganese phosphate and the gas tube material to stainless steel contributed to improved mechanical behavior