Originally Posted by
mic2377
+1 to what IndianaBoy said. There is some latitude to where the gas setting that will allow safe, reliable function. Some configurations are more amenable to this than others, and some companies do a better job getting the gas port "right."
An example of this is my 16" 300 BLK, which has a Noveske pistol gas barrel. Despite having a fixed/pinned block, it runs with 100% reliability in all configurations - subs/supers both suppressed and unsuppressed. There is no doubt that it is probably somewhat overgassed with supers/suppressed, but recoil is not excessive nor is the brass beat up. This is about the most extreme example possible but illustrates that adjustable gas is NOT absolutely necessary.
There is no question that the adjustable blocks are less reliable.