80% ar questions

My nephew is wanting to build a couple ar's off 80 % receivers while I still have a mill for him to use .
He's been rather helpful as I've been cleaning out the shop so I thought I'd buy the tools for him .

Everything I see is for using jigs , so my first question is , what lenght endmills to get ? That's over all gauge lenght not flute .

I should note here that I have a 50 taper machine so clearance for the buffer tower is needed for both pockets

Next is ... is there any real reason to use a reamer for fire control pins over good quality carbide drills ?

You can use the shorter endmills and extend them by sweating them into a shaft to fit your holder. A piece of round stock and the standard end mill may be cheaper than a long end mill and it may be stiffer. If you go this route buy single end end mills as you wont get them out to use the other end

I would use the reamer to get the rounder hole. Drills dont always cut truly round holes.

built a few with friends and family, i use a router to mill and the bit needs to be able to reach the bottom of the lower. normal drill bits work just fine as long as you can drill straight and dont try and push to hard. the fit side to side is more important than top to bottom and use the lockable pins, makes the hole drilling more forgiving.

I'm not worried about what the tools cost , carbide isn't nearly as expensive as it was even 5 years ago .

The reason I asked about drills over reamers is good carbide drills are accurate as to size in my experience. I'm just not seeing a need for a reamer here , on location and size should be good ? Unless I'm over looking something what's a tenth or two going to matter ?

I have only used drills and they worked just fine.
Nothing wrong with reamers, but you really don't need them.
Of course, if you are planning on going into combat with it you would-be better getting a 100% receiver.
I'm not much of a machinist and all my 80%er bubba up receivers work just fine.

I've never used jigs since I have better options.

Here's a print with tolerances. https://cdn.shopify.com/s/files/1/10...52860788957110

I've used mostly HSS or M42 cobalt endmills and reamers for the lowers I've done. I did one test lower using drills and while it did work the fit wasn't as nice as my 100% lowers so from then on I've drilled undersized and reamed the FCG holes. I start off by removing as much of the metal as possible with a 1/2" drill then 1/2" endmill and just use the 3/8" endmill as a cleanup and to form the corners. No need to join the FCG pocket to the rear takedown pocket either if you don't want to. I've done both ar15 and 308 framed ar's (the pocket is the same size). The jigs are nice to use and make it almost idiot proof, but also make the endmills required longer. I generally like to just use the side plates to hold the lower and leave the top plate off for milling like you'd do with just about anything else.

I’ve used the 80%Arms jig with a router and drill press with excellent results. No problem drilling the FCG holes at all.


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Ok I'm not alone in thinking use a good drill and it's good enough , and if I read things right Its gonna need something like a 4" gauge lenght to clear the buffer tower with my tool holders .

buying the Tools is as far into this as I go , sink or swim as they say.

Just so you know, I still suggest buying a cheap drill press jig if you own a mill. It helps make sure you're within spec, and get your cuts and holes drilled in the proper locations. As to endmill lengths, most of those jigs tell you what size endmills you need with their instructions.

like i said before but want to say again, your side to side tolerances are the most critical. my jig gets me close and then i use sandpaper to debur and finish the sides so the internals all fit and are not to tight or to sloppy

I'm not going to encourage the use of a jig , I do get the idea of a visual aid .
But I still have a piece of granite , i will encourage a little time spent to lay things out beforehand .
I might be kind enough to show him how to set up the stops using the Dro before making any cuts .
But mostly I believe I'll stick with the sink or swim philosophy.

Worst case is he screws up and learns something.

Just a suggestion. Check the ATF website for new rules on 80% kits.