Sounds like you have a tiny bit of bolt stick. Its not enough to cause reset problems, but will cause the bolt to start moving a bit slower than it should after it sits for a while. Once the oring gets broken in, there won't be any problems. It can be a pain until then. You can smooth the inner surface of the oring a bit using really fine sandpaper, like 1500 grit. It will remove any surface imperfections and make the oring not so tight.
What is the minimum velocity that your mag will start to cycle using the current bolt spring? If you use the short bolt spring or clip a longer spring to lower the starting velocity a bit, then the higher pressure differential will reduce the bolt sticking until the oring gets broken in.
Except for the Automag in front, its usually the man behind the equipment that counts.