The 17 WSM is a rimfire and has no separate primer. I have had no misfires or split cases in the 20 or 25 gr variants from Winchester that I have fired.
Have you actually tried the ammo? I don't find it particularly accurate in my Bmag but its the only game in town as far as I know.
may I asked how many rounds you have shot ? I have heard people say as high as 20% misfires with Winchester wsm but seems very unlikely I can post my findings for people when I shoot a box of each 20 and 25 gr hopefully this weekend