This is a Elftmann Tactical Trigger known as the Curved, model SERVICE-C.
The ELF Drop-In Service Trigger has been built for law enforcement and military duty. The amazingly short take-up" glass-rod crisp break and next to zero over-travel can be compared to the finest custom 1911 triggers. Adjustability puts you in charge based on your preference. If you are looking for the finest adjustable trigger for your service AR-15 platform" this is the trigger system for you.
Features:
Adjustable from 4lbs to 7lbs without removing from lower
Fits any mil-spec AR-15
Absolutely Drop-Safe regardless of pull-weight