My long range match gun is a old 110 long action. I have had several barrels on it, from 243 Win, to 6x47 lapua, to the present barrel a 6mmBR. Gun shoots great. I would recamend you use a 223 baffle behind the bolt head it shortens up the bolt travel a slight bit, but you don't have to have it. I have a 22BR barrel I bought off of a old member that he had screwed on a long action and shot some very good groups. Fred at SSS took a left handed long action and turned it into a drop port, and he shoots 22BR in it. To answer your first question yes people have mounted 6mmBR barrels on long actions.