Originally Posted by
justin_247
An H-buffer on a carbine length gas system aids in extraction.
Definitely go with the M4 feed ramps if you're using a DD barrel. Arguably M4 feed ramps increase reliability with certain kinds magazines.
Round go on carbines, triangle go on midlength and rifle length, and round notched are for carbines with grenade launchers.
The DD barrel is chrome-lined.
1:7 is arguably better all-around than a 1:9. There's no sense in wasting your money for a 1:9, in my opinion.
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