There are fellas who have and are planning on
doing hopped up loads and cases in the Greener GP,
Martini type action. Here is picture of one done couple
years ago by Aussie guy on NitroExpress forums. They
need heavy barrel in place of original. It has a rifled
Pacnor barrel and weighs about 9 lbs. In my measuring an
action here, they will feed a 3" brass case with a protruding
slug, like the cast Dixie or the Henson jkt slugs.
I like the looks of these old classic guns. And they are
strong enough with 3" RMC brass to get 730gr slug to
2000 fps...Ed

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Ed Hubel