Aero Precision M4E1 Lower Receiver Takedown Pin Set Screw Installation

A Better Lower Receiver

The Aero Precision M4E1 lower receiver is a great product with a number of features that make it better than a basic lower receiver.

The usual lower receiver offers a number of opportunities to mar the finish, snap trigger guard ears off, launch detents into orbit and mangle springs during assembly. 

The Aero improvements include an Integrated Trigger Guard, Threaded Bolt Catch Roll Pin, Upper Tension Screw, Increased Magwell Flare and Threaded Takedown Pin Detent Recess (TTPDR).

It's this last one, that super handy TTPDR, that we're talking about today.

Ready, Set Screw, Go! 

Aero Precision has threaded the channel where the rear takedown spring resides.  

Above: The Aero Precision Takedown Pin Detent Channel Is Threaded For A 4-40 Set Screw

Typically, this spring is pushed in during the receiver extension assembly and held in place by the end plate. 

Above: The Takedown Spring Protrudes And Can Be Mangled During Installation

Due to the Aero Precision design, a 4-40 set screw can be used to hold the spring in instead. 

Above: The Installed Takedown Spring and Set Screw

This accomplishes a few things. It makes it easier to assemble everything with less chance of mangling the spring. It also makes it super easy to swap stocks since that spring will never have to be dealt with again.

Some Tips

Since the set screw will take up some of the space the spring normally would have, you will have to shorten the spring. It's best to shorten the spring by about the same length as the set screw. This will maintain the same amount of spring pressure on the detent.   

Above: Shorten The Spring By The Length Of The Set Screw 

For this project you will need a 4-40 set screw and a 0.050" Allen wrench for it. I used a stainless steel set screw that was 1/8" long and it worked well.

Above: The 4-40 Set Screw Will Need a 0.050" Allen Wrench

No locktite is needed since the screw can't move forward against the spring or backward against the screw.

If you choose not to go the set screw route, the detent spring can be installed just like you would on a normal lower.

Don't Sweat It

The Aero Precision M4E1 stripped lower receiver does not come with the set screw or the wrench for it.

If you have an Aero Precision M4E1 lower but need the set screw, I'd be happy to toss one into any SpiceTac order for you. Just type "Set Screw" into the order comments at checkout. 

If you also need the 0.050" wrench, also type "Wrench". 

Offer good until I run out!