Drop one of those sized cases into your chamber, it should be flush with the chamber face, if it's recessed any, it can cause misfires. To fix the rounds that have the shoulder pushed back too far, you can load them with a start load of your choice, seat the bullet long into the rifling so when the action is closed the case will be flush with the chamber face, then fire form it to push the shoulder back where it should be. I've done it that way, and it works. I have been using a .375 H&H expander to neck up, then size properly in a full length die for my 35 Whelen Improved which has ~.010" too much head space making a standard 35W round very recessed in the Improved chamber instead of flush. You may have to use a 250gr bullet to reach the lands too.
You'll need to adjust the FL die down just a little at time to push the should back to where it needs to be so the round is flush with the chamber face using a straight edge across the face, size then test, adjust die, size and test again until it's just right.
The downward angle of the firing pin can further exacerbate misfires, it isn't inline with the bore, so the farther away from the breech face the primer is, the lower the firing pin hits and sufficiently offcenter pin strikes are a known cause of misfires even if the strike is sufficiently deep.
Tim
