Quoted: Thanks Wildearp. I think Alpha-Romeo3 has covered my confusion on the subject.
What is the purpose of the shrouding on the enhanced carrier should have been my question, the bolt was understandable?
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The bolt carrier on the left is the standard AR-15 and the one on the right is the "enhanced AR-15" and M16 bolt carriers (the other carriers on the right are the same just different picture angle).
The shrouded firing pin design actually was a M16 bolt carrier design.
When they originally designed the AR-15 bolt carriers additional metal was removed on the underside to expose the collar of the firing pin.
This is intended to catch the hammer and prevent firing if the carrier is not fully forward when the hammer releases.
This occurs if the hammer is "riding" the carrier back (i.e. no auto sear is holding back the hammer).
On the M16 bolt carriers, the firing pin collar is not exposed which is the same as the enhanced AR-15 bolt carriers.
LMT, CMT/ Stag Arms and other manufacturers added the firing pin shroud to the AR-15 enhanced bolt carriers to prevent the hammer from rubbing the firing pin collar and causing the firing pin-retaining pin to become bent or break.