Sig55,

Welcome to the forum and well done on your purchase of the 550.
450Dakota is right in saying to strengthen your stock. My BRNO 602 .375 used to shoot dead centre 1.5 inch groups at 100 yards with open sights. One day, out of the blue, it completely missed the target at the range. It was only when I moved the target to 50 yards I could see what was happening. My shots were hitting about 8-10 inches high.
I took my rifle to the gunsmith and luckily could not find any cracks in the stock. He recommended that cross-bolts be fitted and the action/barrel be bedded into the stock. I also had him shorten the rifle a little and added a red Decellerator pad.
The 602 is fitted with Warne QD mounts and a 2.5-8 Leupold scope.
I picked the rifle up from the gunsmith several days ago and haven't yet had a chance to shoot it.