The 80% Arms GST-9 Pistol Built Kit I reviewed late last year was easily the best pistol lower build kit I’ve seen yet. It was window-licker simple and produced a great product.
The 80% Arms Multi-Platform Easy Jig is even better.
The Easy Jig allows the user to turn AR-15, AR-10, and 9mm GLOCK compatible AR platform 80% lower receivers into finished lowers. It fits any “mil-spec” lower, and you can use it over and over again.
You’ll need a few tools to do the job, but just a few. Most important is your router. Something like a Dremel or rotary tool won’t work, you’ll need a bit more power than that. You don’t need anything special, though, and there is a router compatibility chart posted on the 80% arms website.
You’ll need a real drill, not a glorified screwdriver. You do not need a drill press. You’ll also need a vise, and the bigger and sturdier it is, the better. You’ll also need a single Phillips head screwdriver. A shop vacuum is also highly recommended. Beyond that, and some vegetable oil, everything else is provided.
If you’d like to watch videos of the entire process, you can do so on the 80% arms site. I did the project without ever looking at the videos. I just following the supplied instructions.
Even if you have zero mechanical aptitude, as long as you follow the very clearly laid out instructions, everything’s going to go fine. 80% arms has created a project that is essentially brain-damaged-old-redneck-proof (ask me how I know), and that’s saying something.
First, put everything together. That means installing the guide plate on your router and putting the jig together. This was the most challenging part of the entire process and it’s super easy.
The genius of the whole thing is that top plate on the jig. You can mount any of the receivers to it, depending on what holes align. This part is pretty much impossible to screw up.
After that, you’ll need to mount it on a sturdy vise. I decided to do all of it outside in an area where I wouldn’t care much about stray aluminum shavings, so I just screwed the board one of my vises was mounted on to a sawhorse and got to work.
Once the receiver is mounted into the vise and, again, the instructions are extremely clear here, you’ll need to drill your first pilot hole. The instructions tell you exactly what bit to use. But wait, you say you don’t know what bit is what size? The bits they sell have the size printed on each bit for you.
The instructions make it clear that you should be using a cutting oil. You could absolutely get away without using any cutting oil on this process. This is hardened steel bits vs. aluminum. But you will get more miles out of those bits, and probably a cleaner cut, if you go ahead and liberally apply some cutting oil.
I used simple vegetable oil, which works perfectly well. A spray bottle is nice, but just pouring it on the bit and receiver works just fine, too.
Once the pilot hole is drilled and the guide is removed, it’s time to start the work with the router. You’ll see the intelligent design of the jig here.
There are three sets of guide pillars of different height on the top of the router. These correspond to three different depths of section on the top of the jig. You’ll also find a handy little set of three hashed sections on the corner of the surface of the jig.
The shortest pillars go first, cutting the largest section. Put the router on top of the jig, with the router going into the guide hole. Use the hashes to go bit by bit, making pass after pass.
Follow the suggested pattern in the instructions. Between each pass, use a shop vac to remove shaving from the jig surface, receiver, and the router guide plate. After you’ve removed all you can, use the hashes as a guide to lower the router cutting bit a little more, and do it again.
Take your time, taking only one hash mark worth of metal off each time. When you’re done making the last pass on the last hash mark, you go to the next longest set of pillars, do it all again, then use the longest pillars and do it all a third time.
And you’re done. Spray it all off, clean and deburr it with a hand deburring tool. That’s it. You now have a “firearm.”
The first AR-15 lower receiver took me a total of 2½ hours to complete. That included a drive into town to buy some vegetable oil from the Dollar store and, while I was there, a dipped cone from DQ and a couple of chopped beef barbeque sandwiches (extra pickles, extra onions). The actual work time was closer to an hour.
The next two — a .308 and a 9mm lower — took me 90 minutes total for the both of them, including the deburring and cleanup. In a single afternoon of light work, I machined three firearms, had lunch and some ice cream. That was a very good day.
I’m still waiting on parts to finish the AR-10 and the AR-9, but I had enough laying around to build out the AR-15 lower and match it to a few other AR-15 platform uppers. I had some mostly milspec-ish parts laying around, and assembled the AR-15 lower using those.
Everything fit great. When compared to actual MIL-STD specs, the trigger well came out 15 thousandths of an inch wide and the takedown lug pocket was 10 thousandths over spec as well. Everything else was dead on perfect.
I’ve seen lowers completed where the selector pin hole or takedown pins weren’t just right, but I had no such issues here. The disadvantage to the slightly oversized trigger well is that the trigger has a bit of wiggle room to move around. The advantage is that any trigger will easily drop in and fit.
Note the little green button-looking thing near the buffer tube. That’s the screw that exists on some billet lowers that allows the user to insert it from the bottom, screw it up, and add pressure so that the upper and lower mate tightly. It’s a nice, but not always necessary addition.
So how does it run? Like a spotted ass ape.
Does a SIG MPX upper receiver, with its dual captured spring system work on the 80% arms lower? Yes it does, and perfectly.
Does a Daniel Defense 6.8 SPC upper fit and work? Yup.
Does an upper from a $10,0000 hand engraved one-off art AR from Underground Tactical fit and work? Yes, and the combination is a spectacular amount of ridiculousness.
I also ran a bone stock direct impingement Colt Competition upper on the 80% Arms lower and put it through its paces. It worked flawlessly. The takedown pins are a little tight, but that’s a heck of a lot better than loose. You’d have to look pretty close to suspect it was done at home on a router, and not a big brand commercial CNC machine.
I ran a cheap trigger and whatever mixed trash I had laying around to complete the lower, but if you wanted to fill it up with a better trigger and upgraded internals, they wouldn’t be out of place at all.
At the end of it all, the jig and the tools, including the drill bits from 80% Arms, are still in great shape, and ready to do more work. If I had a dozen lowers, I have no doubt I could make a dozen more good, very well performing lower receivers with this kit.
There is a current back-order on the 80% Arms Multi-Platform Jig, as well as all of the 80% lowers. 80% Arms notes on their website that they are currently shipping orders for these items that were placed in late November of 2020. Even if the current national political climate wasn’t hostile to firearms, I have no doubt these would still be selling out.
The 80% Arms Easy Jig Gen 3 Multi-Platform jig works. It’s an elegant piece of kit, able to solve several problems at once. It’s precise enough for the job, reusable, portable, and makes all of the major AR platform lower receivers.
So far, so very, very good. As soon as I finish the AR-10 and AR-9 uppers and get in some lower receiver parts, I’ll finish those and do an update on them as well. I have no doubt they’ll run just as well as the AR-15 receiver has.
Easy Jig Tool Kit
Billet AR-15 80% Lower
Billet AR-10 80% Lower
Billet AR-9 80% Lower
Overall * * * * *
I think I spent more time standing in the kitchen trying to figure out why I came in there this week than I did building these lower receivers. 80% Arms continues to impress me with the clear instructions, ease of use, and overall great final products. This is kit that’s very much worth the wait.