jonr - lefty o and victorcharlie have given you good advice. Most often it is the 'fit' of the parts that cause accuracy problems. However, that being said, I used an Ed Brown accuracy barrel and bushing in my SA GI and watched my groups drop from 7", 7" high and to the left, with a number of different mil-spec barrels, to 2.5" at poa (bullseye) at 25 yds with ball ammo.
I would see if a quality gunsmith can fit the factory barrel to the slide better than it came from the factory - that might just be enough to improve your accuracy to your satisfaction without the $200 for a new barrel and bushing. HTH. Mikey.