What can I do to help my new M1A standard to shoot better than 4to5 inch groups

[vintage hunter]

If your referring to the guard swinging open that's normal. That's how you break the rifle down into it's 3 main groups.
Lock up refers to the amount of clamping force the action/trigger group puts on the stock. When re-assembling the rifle you should begin to feel resistance when the TG is about half way closed.
Do you have a Springfield Armory M1A? Was there no information guide with it?