M1 Machining 80% AR-15 lower receiver review


M1 Machining 80% AR-15 lower receiver

Price - $110
Material - 7075 billet aluminum
Finish - anodized
Color - black
Rear pocket - not completed
Trigger guard - integrated
Engravings - Safe/Fire (printed, not engraved)
Notable features - flared magwell, safety selector stops, threaded hole for bolt catch pin, magwell gripping
Works with the 80% Arms Universal Easy Jig - yes

Works with the Modulus Arms Jig - yes


M1 Machining 80% lower receiver left sideM1 Machining 80% lower receiver right side

M1 Machining 80% lower receiver topM1 Machining 80% lower receiver bottom


First impressions:
This is a nice looking design with well done anodizing. Overall it is reminiscent of the 80% Arms lower with some additional features. Specifically the machined magwell front gripping, threaded bolt catch pin hole (not such a great feature it later turns out) and a few other reinforcements. It has an integrated trigger guard and flared magwell found on most billet machined lowers. The safe/fire markings are not engraved but are printed in white.


Fitment to the universal Easy Jig:


M1 Machining lower fitment to 80% Arms Easy Jig


Fitment to the Modulus Arms Jig:



Ease of machining:
As noted with the other 7075 lowers this material is tough stuff. The polymer, 6061 and A380 receivers gave no problems with the drill press set at 1720 RPM. But that speed was a no go with this material. I had to drop down to the lowest speed of 620 RPM to make any real progress. Judicious use of cutting fluid was also needed. Once I switched to the router I saw no real differences between this and the previous aluminum lowers. But when removing massive amounts of material as you do in the first steps with the 3/8" drill bit it will be very clear. If you have a lower powered drill press as I do you will want to take frequent breaks to keep your drill press motor from burning up. I have also found the key to getting through without binding is getting the speed and pressure on the bit just right when using the drill press. It takes some experience but when you get it just right it works great. I don't even use cutting fluid anymore.


Final thoughts:
No surprises in machining this receiver. The beauty of the Easy Jig is once you have the lower aligned in the jig it's almost idiot-proof.


I did have several issues during the installation of the parts kit. The first was the hole for the pivot pin detent spring. I couldn't figure out why the spring wasn't dropping down so I pulled out the spring and it had bits of grit on it. I used a small screwdriver to loosen up the grit in the hole and then used the spring as a grabber to pull the grit out. It took a while but I eventually got out at least enough of the grit to install the pivot pin properly. I assume this grit was stuck in there from the blasting or tumbling done to the receiver after machining but before anodizing.


I also had an issue getting the magazine release button in. The button would drop in all of the way flush with the receiver but then stop even though there was plenty of room left behind the button. This was an issue because you need the button to push beyond flush in order to properly set how far the button sticks out. I tried a different magazine release button, both standard buttons, and that one dropped all of the way in. I've never had that happen before. It was almost as if the hole was slightly cone shaped where the bottom was narrower than the top. Others have reported this problem as well.


After assembly I tested several magazines for fit. Most GI-type magazines fit fine. However I cannot get a Magpul PMAG, Lancer Warfighter and even some metal magazines into the magwell at all. Not that they will go in but not drop free. They won't go in at all. Here is a picture of how far a PMAG will go into the magazine well. It turns out these magazine wells are not broached.


M1 Machining 80% lower receiver PMAG doesn't fit


There were other issues as well. The safety selector detent hole seems to be misaligned so when the selector is on "FIRE" it points to the eleven o'clock position rather than twelve o'clock.


M1 Machining 80% lower receiver safety selector problem


A Magpul MOE grip will not fit the lower because the beavertail of the grip runs into the bottom of the receiver. Note the gaps below which don't allow you to install the grip. I have also tried a Hogue rubber grip and the safety selector catches on the grip.


M1 Machining 80% lower receiver MOE grip problem


Another user online reported that the bolt catch slot on their receiver was machined too far back so the bolt catch isn't pushed up by an empty magazine. So basically the bolt won't lock back on an empty magazine (pic below). I don't know if my lower has the issue because I've never been able to install the magazine catch due to reasons outlined below.


M1 Machining 80% lower receiver bolt catch problem


On top of all that the lower requires a special bolt catch pin that was not included with the 80% receiver I was sent. I contacted M1 Machining and was told seven weeks ago a pin would be sent. After another week and two emails I was told an order of new pins was just received and my pin would be sent "tomorrow". Three weeks after that I was again told pins had just come in that day and my pin would be sent "tomorrow". No explanation of why I was never sent a pin as promised the first two times. Four weeks have passed since that and still no pin. And since it is a proprietary pin I can't just go buy another. I have since determined that the threaded bolt catch pin sold for DPMS 308 AR uppers will work with this lower. They are pricey and run about $4-5 a piece. The DPMS part number is 308LR12 (Brownell's) or 308-LR-12 (MidwayUSA). Between the magwell problem and all of the fitment issues I basically now own a fully machined paperweight.


Due to the issues with the magwell, receiver tolerances, fitment issues and general lack of customer service I cannot recommend purchasing this lower.


80% lower receiver comparison chart