Use a small amount of break-free just around the head, ( because paint and corrosion can bond the heads to the retainer bars) then use a square tipped gunsmith's screwdriver tip, not a standard tapered one. It must fit squarely and exactly.
Laying the rifle on a towel flat on the table,give the screws a very slight bit of pressure clockwise
, then with full downward pressure
turn them counterclockwise to remove them. If the screwdriver isn't the right fit you'll ruin the heads. If that happens contact Guisan here..... http://theswissriflesdotcommessagebo...MINISHOPS.html
He'll send you replacement screws. Its not hard to doi but you have to take your time and definitley use the right driver.