^this, plus Mega and the custom billet stuff by companies like Seekins Precision.
All AR lowers are aluminum, unless they're the polymer or carbon-polymer versions. Stay away from non-aluminum AR receivers, both lower and upper.
DinanTronics Stage 1 F30 328i M Sport
Dinan 20" Black Performance Wheels
Gunfighter Training Development and Evaluation
AR15/AR10 Armorer/Advanced Armorer
Gunfighter Training YouTube Channel