A Marine with 3rd Battalion, 11th Marine Regiment, fire a 155mm M777A2 Lightweight Towed Howitzer in the Lead Mountain Training Area at Marine Corps Air Ground Combat Center Twentynine Palms, California, May 3, 2016. This firing exercise was focused on the ability of the M776 Chrome Tubes to resist the formation of hardened downbore residue when firing the M232A1 Propelling Charge 5H (top zone charges). - A Marine with 3rd Battalion, 11th Marine Regiment, fire a 155mm M777A2 Lightweight Towed Howitzer in the Lead Mountain Training Area at Marine Corps Air Ground Combat Center Twentynine Palms, California, May 3, 2016. This firing exercise was focused on the ability of the M776 Chrome Tubes to resist the formation of hardened downbore residue when firing the M232A1 Propelling Charge 5H (top zone charges).