Part of the problem was the skinny barrel on the old ones. Not very rigid so it would vibrate like crazy and throw your shots off. I found I could improve accuracy by just adding a flash suppressor.
Then someone came out with the Accu-Strut which stiffens the barrel even more. Gives it an M-14 look:
This one isn't mine but you get the idea: 
The newer ones have a heavier barrel which should help. Haven't shot a new one either.