My Lajot o/u 9,3X74r is amazingly accurate with factory Sellier & Bellot ammo, and does OK with RWS, not quite as well with Norma...

The point is, that AMMO can deternime how any rifle shoots, and may give a false result of the actual inherent accuracy of a given rifle. Double rifles/double so...

o/u or sxs...I find no difference.