I suppose the old XM177 style with 11.5" bbl, and carbine gas system must work fairly smooth.
I never saw much sense in the 11.5" bbl with a welded on long flash suppressor to make 16", but I would imagine it's fairly easy on the internals given the shorter dwell time.
I've never heard of the longer flash hiders being better either. Just longer so they're legal.
