Grandveneur,the other post-1952 models MC and MCA were named for their buttstock shape, Monte-Carlo and Monte Carlo Amerikanisch, both have swept-back bolthandles too. So a "Gebogener Kammerstaengel" = swept back bolthandle was no distinguishing feature between the three models MC, MCA and GK. The designation "GK" is also found on 6.5x68 and 8x68 Magnum rifles with blued, straight bolthandles and straight buttstocks, as made for the European market. So I rather believe "GK" stood originally for "Grader Kolben" = straight buttstock.