Soldiers of the Army’s 1st Infantry Division at Fort Riley are converting to a new model of the M4 carbine used in combat.

The division is the first in the Army to begin converting to the new weapons. The Army expects to replace about 500,000 carbines through 2020. Fort Riley soldiers are expected to continue converting to the new model through June.

Fort Riley officials say the new version, called the M4A1, has a slightly heavier barrel that withstands heat and gives soldiers a longer rate of fire. The newer version weighs slightly more than the standard M4 which is attributed to a backup sight, forward pistol grip, empty magazine and sling.

The M4A1 has been used by the U.S. Special Operations Command since 1994.