5.56x45 C.A.P.S. Mid-Length Piston Upper with Magpul MOE M-Lok Handguard

A: It is not a drop in fit. It would require some material to be removed so it would fit around the gas block

A: It's not a drop in as it would have to be modified to work with our piston system.

A: Great Question!
C.A.P.S. = COMBAT ADAPTIVE PISTON SYSTEM (we do list these features under the C.A.P.S. Product Feature Tab):
4 Position Regulated Gas System
Pull Through Gas Block Design
Ambi-Regulator Knob
360° Continual Rotation
Easily Adjustable with One Hand
Easily Adjustable with Gloves On
Easily Adjustable from Firing Position
Audible and Palpable Setting Confirmation
No Detent Pin to Push In to Adjust Gas Regulator
Regulator Knob Allows for Zero Visibility Adjustment
Interlocking Mechanism Prevents Accidental Rotation of Knob
Knob Configured for Rapid Adjustment with No Loss of Target Engagement