Definitions for "rimless"
A case head type; actually a misnomer. Rimless cases have a rim, but it is the same diameter as the case body so it does not protrude. An undercut extraction cannelure or groove provide a surface for the extractor to grip. Example: 30-06 Springfield
lacking a rim or frame; "rimless glasses"
Frames in which the lens appears to not have a frame, held together by invisible nylon cord, notches or mounting screws.