Once you have determined that the FA has the accuracy or is in the ballpark of your expectations, the biggest variable after that is ammunition. The ammo can vary in performance by type and by batches within a type. In other words ,don't expect the same performance from brand x of successive batches. An equipment change (like a barrel) may work with one type of ammo but may behave completely different with another type.
Performance improvements may result from various modifications,( eg trigger,bedding,floating a barrel etc) but there is no way of determining the degree of improvement.
Rather than trying to make a silk purse from a sow's ear , you would be better off spending a little more to get something that has a better reputation.