The invention relates to a support member for supporting a shell into the barrel of a breech-loading weapon, and a method. The support member (6) comprises means for fastening a support element (8) to at least one fin (5) belonging to the tail end (4) of a shell (1). The means comprise at least one fastening piece (10), which comprises: at least one first fastening surface (14a), which may be arranged substantially parallel with a side of the fin (5), and which fastening piece (10) may be supported to the support element (8); at least one second fastening surface (14b), which second fastening surface (14b) is movably arranged so that the second fastening surface (14b) is movable in relation to the first fastening surface (14a) in a direction transverse to the longitudinal axis (L) of the shell (1); and means for pressing the fastening surfaces (14a, 14b) against the sides of the fin (5) arranged between them so as to provide friction locking between the fastening piece (10) and the fin (5).