Yes, the adjustable carrier does work to reduce bolt velocity, however there are a couple side effects.
#1 the adjustment mechanism leaks and reduces the gas drive in the "normal" setting.
We tested this back to back with a BCM BCG.
The mil-spec BCG produced 2:30 ejection and the adjustable BCG produced 4:00 ejection and notably slower bolt velocity.
When sizing EZTUNE gas tubes, we go up one size to compensate and get the same level of Gas Drive.
This isn't a huge deal, but isn't exactly expected either.
For over gassed uppers, this leakage could actually be considered a benefit.
#2 the gas venting in the suppressed setting is directly adjacent to the shooter's ear and extremely loud.
Again, we tested it in the full suppressed setting without a suppressor attached.
The bolt didn't move or eject the brass, as expected.
What wasn't expected was the notable ear ringing / discomfort in one ear through the usual
Surefire EP4 hearing protection.
Again, this was without the suppressor attached, so it should represent the minimum level of ejection port noise produced.
The EP4 are admittedly not "heavy duty" hearing protection, but are completely sufficient for all other shooting.
#3 It requires a tool to adjust.
This may be a minor quibble, but Murphy's Law is in full effect whenever you're in the field.
In summary, the adjustable carrier is a viable solution.
However, in many cases it's simpler and easier to setup an upper for 50/50 suppressed use and (optionally) just swap in a heavy buffer when suppressed.
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