I recently purchased a 80% lower to build my first ar15. To complete this receiver  you must drill out the trigger, hammer pin holes, the safety selector hole and mill out (or dremel) the FCG (fire control group) pocket. I recommend that you do this first (although it is not necessary to do first but it will make it easier). I strongly recommend clamping the receiver in a vise to secure it during the drilling process. Make sure to step up the drill bit sizes start with a 3/32nd bit for all three holes. Next using a 5/32nd drill out all the holes remember that you only go about half way through the receiver, drilling from both sides. Now the trigger and hammer pin holes are complete , the selector hole needs to be bored out to 3/8ths I would recommend that you don't jump straight to this size, but if you do drill slowly and carefull. Now here it's the part I have run into a problem milling out the white plastic. I don't have a mill, or a drill press with a cross sliding vise (yet). So I used my dremel rotary tool. I took my time removing the wit plastic being careful not to go to far through. Then in an attempt to fit my FCG parts in quickly realized they wouldn't fit. So I sanded and filled slowly stopping ever so often to try to fit the FCG parts , but then DISASTER strikes I removed a little to much plastic in the front of the FCG pocket breaking through to the magazine catch/release spring housing! Please someone anyone help can I repair this.with some kind of epoxy???.......

I believe JB Weld is your friend.

Serial number and paper work, or lack thereof.

Yea i hear ya. Some people just like having a lower that isn't on any type of list if there is ever a gun confiscation or whatever, (paranoid)and some people just actually enjoy doing the work and things of this nature lol

I am doing this project because I enjoy the work and getting some more experience in the gunsmithing field

If you bothered to read my title and whole post you would see that it is a polymer lower not metal

I would stand behind a steel plate the first time you TRY to fire it  Plastic or metal, doesn't matter, no one can perform precision machining with a hand drill and a die grinder (Dremel.)



Building things without the proper tools only leads to failure.

An AR lower does not have to be a precision thing. Admittedly an hand drill and a Dremel is a stretch, but a drill press will work just fine. As for the OP, may not be able to fix this one.  



 

Needs pics.  If the break through to the mag release is small enough there won't be a problem except dirt can get into the spring area easier.  Any two part putty epoxy should work.  Jb weld may work.  I use a two part epoxy to bond and repair plastic prototypes.  It looks like 2 colors of play dough in a cylinder, one wrapped around another.  Cut off a piece, need together until color changes, then apply.  It's sold as a way to seal water line leaks. Oatey fix-it stick is one brand of the two part rigid epoxy.

Um because some people want guns that don't have a 4473 form with their name on it.

It's a lower , not a barrel.  You couldn't screw up a lower bad enough for it  to blow up.

That putty may hold water, but nothing else.  Use 2 part Loctite Plastic Epoxy from Wal-Mart, Lowes, etc.

I recently used that putty to attempt to hold an AR buffer tube inside my platic brick stock.  It did not work.  Tried again w/ 2 part epoxy, and where I applied the not-cheap epoxy, it held up.  The psi ratings on the packaging of the two products are an order of magnitude apart.

ETA:  OP, I may be in the boat right behind you.  Looking @ Dremels & their 2" micro-drill press attachment right now, to have @ my Zombie Green $35 blem EP lower.

I used two part epoxy (j b weld) it seems to do the job. I even (accidentally) dry fired it while fitting the hammer and it held up just fine

The 2 part JB Weld epoxy would seem to be equivalent to the Loctite 2 part epoxy series, and is twice as strong as the 2 part putty.  It's also significantly cheaper than the Loctite, so I'm thinking of using JB Weld on my next stock, see how it does w/ ABS plastic.