Di collar or grease collar is seen in -

The synopsis of forensic medicine & toxicology ; Dr k.s narayan reddy ; 28th edition ;pg.no 131 A di collar is seen in firearm entry wound ,it is seen as narrow ring of skin ,lining the defect & is sharply outlined . This results from the removal of substances from the bullet as it passes through the skin ,i.e bullet lubrication ,gun oil from the interior of the barrel ,lead from the surface of bullet ,barrel debris etc .