ZG-47's from 1956/57 are usually better machined and finished than later ones from 1961/62. I had perhaps 10 zg-47's over the years. Brno 600 series are often great untill 1968 or 1969 after that the quality begun to swing greatly. Brno model 21 and 22 can vary one rifle to the other.

I think the zg-47 receivers were machined from forgings and bolts before 1958 has better maching then later ones. Bolt shrouds are cast.

some of Brnos from end of communist era 22lr and 222 etc. were with cast actions.