I took a student’s carbine that was completely dry and showed how I lube an M4 without taking anything apart by dropping oil in the bolt carrier exhaust ports then firing 5-7 rounds. Obviously, this is mostly used in training although some have used it for real. This will lube the necessary parts of the DI M4 system without putting oil where it doesn’t need to be or having oil dripping onto the top of the magazine. Been doing it for years.
*Photo courtesy of Defoor Proformance Facebook page