The line is short for mainline. Mainline is the general population of a prison. Metal cuffs with a two or three foot chain, designed to be placed on a prisoner's ankles to control the movement of his legs, and prevent him from running. Inmates are locked inside their cells for an extended period of time for security reasons, such as after a major or several smaller incidents. During a lockdown, normal inmate programs are suspended and inmate movement is severely restricted.
Inmates eat in their cells and showers are restricted to one cell at a time, instead of groups.
The small .223 caliber bullet is the same one that is fired from the military's M-16. Rugger also makes a Mini-30 that is chambered for the 5.62X39 round, but CDC does not use this riffle. We also simplify the term Cell Move to just Move. An MTA is basically an LVN with a badge. Although there are some MTAs with RN licenses, the department will not allow them to perform duties above LVN level.