I don't use a scope/optics on my Saiga 223, so I can't help you with that part ...
But, at 100 yards, I am reliably putting 100 rounds in a 3" circle with 2-3 fliers.
At 300 yards, you should be easily hitting COM on a man-sized target 90% of the time from prone with a bipod, and 75% of the time prone without bipod.
Usually, the best thing you can do about improving accuracy of your rifle is to practice.