I would say that you are shooting pretty good considering your setup.
When I talk about shooting really good groups it is from a rock steady bench and rest. Like you I can not shoot a 1/2 inch group every time even with a custom rifle. A lot of folks will get one group that measures sub 1/2 and claim that they have a 1/2 inch weapon. Its a bit misleading to say the least, there are so many variables to consider wind being the most prevalent. With my hunting weapons I likea gun to shoot consistantly 3/4 MOA or under. I have a 6.5-284 that will shoot 1/2" groups at 100 yards from the bench all day long If (and its a big if) I don't screw up. You know a little flinch or pull can turn a sub 1/2 into 1 1/2 in a hurry. From hunting positions I would be happy with anything close to 1 inch.