I have seen a couple on our range and they seem to go bang and hold up well with other brand names in accuracy. I think it was PB bullets(the company that make dead centre, etc.) that tested the win. 150 on a bou hunt in Quebec and stated they performed flawlessly.
As far as open breech, does it not have a weather shroud? I have a Rem 700MLS and it came with a weather shroud, so you might want to check if their is one available and it is legal. If not a wool sock will help keep moisture off the nipple and breech area. just remember to remove it before you pull pin
! Also in wet weather tape the end of the barrel with electrical tape to prevent moisture from entering.