breaching round or slug-shot is a shotgun shell specially made for the purposes of door breaching. Breaching rounds are designed to destroy door deadbolts, locks and hinges without risking lives, and are used by military and SWAT teams to quickly force entry into a locked room. Breaching rounds are frangible, i.e., they break up into fragments, and are made of a dense sintered material, often metal powder in a binder such as wax, which can destroy a lock then immediately disperse.
That means after a shotgun has fired a breaching round, it should leave a residue of metal powder.
In a video uploaded to YouTube by “Barry Soetoro,” it is claimed
exactly that metal powder residue can be seen surrounding bullet holes
left on a wooden magazine rack in the foyer of Sandy Hook Elementary
School. The rack was right next to a large glass window that the FBI
claimed Adam Lanza had shot and shattered with his rifle on the morning
of December 14, 2012, to gain entrance into the school.