I stand corrected on the 'subsonic' issue. However, the adjustable gas system is still advisable because of the variance between certain kinds of ammunition (ie. Wolf v. American Eagle).
Paul not really if you were to look at the AK system the eastern bloc ammunition is very far from a true standard of performance an yet the AK system works very well . If one were to look back at the development of the gas piston operating system you will find we have come pretty much full circle meaning that many of piston drive firearms are using non adjustable systems . Many manufacures know more about the piston drive systems and how to make them work with out requiring an adjustable system which adds costs and yes frustration to the user.The other reason is quite simple ammunition variances in performance have improved dramitcally since the 50's.


















































