I've been using Norma shells. Specifically one called "Nittedal Spesial" in US# 6 and 7. (I don't think these have been available abroad?). This is basically because I've had quite a lot of them laying around!
16 gauge shotguns (and ammo) are becoming less and less common over here which is a pity cause they work well on these types of birds. Nowadays it's 12 and 20 gauge that dominate.

From this year on, all lead shot is forbidden here in Norway, so people with older 16 gauges that can't handle steel shot will have to go over to Bismuth etc. That is if they don't have a stash of "illegal" lead shells...

Just make sure you don't get caught using them!

In 20/76 I've mostly used Federal ammo, although early in the ptarmigan season I use 20/70 cheap trap ammo since the birds fly up pretty close.

I like using a 20/76 gauge since with the hunting up here, the shotgun is carried more than it is shot... The light weight makes hiking all day no problem. Not that a 12 gauge is heavy for a grown man, but a kg or so lighter is nice no matter how big and strong you are IMO!

Erik