I agree - as far as I know the gape is determined by the cartridge diameter rather than length. Therefore the choice of S/S or O/U is a subjective one and explains why alot of people (like me) like O/U small guage shotguns and S/S 12 bores. I don't have an O/U DR though, but have seen them used alot for monteria (driven stag/boar) shoots in Spain in calibres up to 9.3x74. Haven't seen larger calibres in the flesh, so to speak