The classic grouse gun is a S x S in a small gauge , short barrels & open chokes . I agree with this classic after
hunting them since 1962 . My best , so far , is an AYA Model 3 , in 28 ga. Next are my Ithaca Flues in 20 ga.
& 16 ga. Some prefer O/U , but not me . ,,,,,,,,,,, my 2 cents.