Some cleanup was necessary with a sharp, carbide machinist's scraper inside the selector hole when installing a standard lower parts kit
Since the PSA upper receiver assembly was pre-assembled, all I had to do was put the lower parts kit
in place and add the stock.
The AC-15's Gen 2 lower receiver has a flared magwell and upper tension screw and includes an MSR Lower Parts Kit
and an MSR/ M4 Buffer Kit.
Some are supplied in kit form with a fixture, tooling and even a lower parts kit
while some are simply a standalone lower.
To fill out the lower receiver, I got a DPMS lower parts kit from Brownells.
Another brand of lower parts kit I like and use a lot is offered by J+T Distributing (Double Star).
Plus, most importantly, there are those two magic things in the lower parts kit called "receiver pins" that allow anyone to install and replace the entire top end of an AR-15 in seconds.
When it came time, I sat my son down and had him empty the lower parts kit into a clear plastic tub just so he could see all the pieces and they wouldn't roll around and get lost.
Since I had previously GunKoted my upper and lower receivers with matte gray GunKote, my lower receiver only needed to have the lower parts kit
installed in it.
With these measurements in mind, he tweaked the design of the mold so that virtually every lower parts kit would fit into the finished product.
In the dozen or so I've made, each one has presented zero problems when installing a lower parts kit or inserting a variety of mags.
Along with the upper I ordered a couple charging handles, a complete bolt assembly, complete lower parts kit
, a few firing pins, extractor springs, extractors, ejector springs, ejectors, cam pins, firing pin retaining pins, buffers, buffer springs and gas tubes.