Installing the forward takedown pin and the detent and spring that retain it in the lower is arguably one of the trickiest aspects of putting together a stripped receiver, but the Real Avid AR-15 Pivot Pin Tool makes this task an absolute cakewalk.
With the Real Avid adjustable Smart-Fit Lower Vise Block locked into the magwell and vise, we chose to install a Velocity Triggers extended, two-piece VRM Magazine Release instead of the mag release in the lower parts kits. Available in many colors, the VRM a definite improvement over its Mil-Spec counterpart.
Aero Precision is also a vendor for other manufacturer’s quality components where it makes sense, and the Geissle Super Dynamic 3-Gun Trigger we acquired through them is a good example. With a short, light (4-lb.) single-stage pull and short reset, this trigger is very well suited to rapid and precise target engagement.
Another time-saver Aero incorporates into the M4E1 lower is a threaded rear takedown pin detent/spring bore, which ensures a clean install of the buffer tube/receiver end plate without the detent spring taking flight and ending up in the neighbor’s yard.
The next pieces of the puzzle include the buffer tube and receiver end plate, which are attached to the receiver extension via a castle nut. Here, again, we used blue Loctite and the Real Avid Armorer’s Master Wrench to snug things up. The buffer tube is now ready to receive the buffer and spring your configuration calls for. In our case it was a heavy (H) buffer.
Your lower is now ready for the safety selector, the detent and spring that hold and retain the selector and the handgrip that retains the detent and spring. Note the black tension-adjustment screw sitting directly behind the threaded grip-screw bore, which allows you to take up any play between the upper and lower receivers.

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