What Tim is trying to say delicately (he is such a good guy!) (I, on the other hand have no problems telling you what's what)- you need to experiment to find what works for you. You are going to have to find what works, no one can tell you what, will work. There are plenty of ideas in the FAQ section. Roll up your sleeves and start to work, this is unfortunate, but that is just the way it is. You will just have to try different things until you find what works. As has been suggested before; just do one thing at a time, so if it makes the problem worse, you can undo it.
These are production guns, not fine works of art - so lugs are not going to be always straight, or square or what ever. If any of these conditions exist that effect accuracy, then they are easily corrected. This does not always work, but in general I have found that the barrel must be tight on lock up and a little loose when not -you will have to find out yourself what works. I do wish you Luck and Good Shooting as well.