.222ND
No one can help you with this problem unless they own one of the Sako PPC USA rifles. I have the same rifle in 6PPC USA and have had the exact same problem with gases blowing back on the shoulder and even down onto the body of the cases. If you check I have a thread on this very same problem, in a couple forums actually. I tried everything imaginable to fix this blow back problem. I asume you will be reloading for this gun? First thing you want to do is take the Norma brass that is blowing back and toss it in the garbage. You'll need some brand spanking new brass, preferably the Sako 22 PPC USA brass that was made just for these guns, if you can find any, which you may not find any, maybe someone reading this can help you. I recently bought some of the Norma 6mm PPC headstamped brass and found that after the first firing I had no blow back problem. When I bought my Sako 6PPC USA rifle, I bought enough brass to hold me for a while, and recently I prepped out 60 cases of this new brass and after first firing had no blow back. I had this same brass that had been fired many times and I guess became work hardened and I got blow back and tossed them in garbage. I also tried the Lapua 220 Russian head stamped brass brand new and with this brass I got blow back, not sure why. I normally shoot brass many many times and never had this problem, only with this Sako rifle. So get some new brass and let us know how it works. If you need help with loads and anything else just yell. Just one other thing, these Sako PPC's are really great guns and they are the most accurate out of the box gun ever made, I know mine is. I hear the cow bells.
Dave T