After flipping thru a S&S catalogue, it would appear that the Modell XXIX(S) may have changed. In this particular catalogue the images of the S&S Modell XXIX(S) is actually a Selbstspanner Taubenflinte(Seitenschlossen) or Sidelock Pigeon gun so the S would denote Seitenschlossen?

Cheers,

Raimey
rse