I have tried different magazines and the problem still occurrs, also there seems to be an occassional problem when the action cycles put the firing pin will not strike the primer on the follow up shot. Regards Steve
ps ammo is south afrikan 55gr.
Something sounds really screwy here.
Try different ammo first- SA ammo will be on the hot side if anything.
If the firing pin isn't striking, it might be because the bolt isn't locking all the way- either you have a dirty chamber, a headspace problem (not likely but possible) or the ammo is out of spec.
Who or what company assembled your upper?