Fitting an AR15 Colt Mag Adapter

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  • Ggreen

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    Sep 19, 2016
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    AR building is pretty much like playing with lego's, until you go a little off the beaten path. MilSpec rifle caliber builds are generally straightforward due to parts being built to a standard, but with AR9's you get into a world of small batch parts and custom fitting on the installers end. Personally I have found that the colt mag is the most reliable, fast and affordable way to have a competition worthy ar9. Glock mags are double the cost, single feed, have complex mag release mechanisms, complex bolt hold opens if any, and they must be inserted at an angle for them to properly feed a round into the chamber. The colt mags feed straight up, have cheap reliable and widely available steel 32rd magazines (18 dollars is the most i spend) with + 10 extensions being available for around 30 dollars.

    The problem with colt mag ar's is most people buy as cheap as they can and expect it to run like their 400 dollar psa in 223. It's just not that easy, some may get lucky, most end up with a headache. My general rule with non standard ar's is that you get what you pay for. Macon Armory is currently the only ar9 magwell adapter manufacturer i recommend, and the most expensive. They basically drop in and require a 5 minute ejector adjustment to run perfectly.

    For this write up i went with a cheaper option. AR Stoner magwell adapter is about the standard cheapish ar9 adapter on the market. In pictures it looks nearly identical to the macon, but there are key differences that make it a real pita to install and get to run reliably.

    I didn't take a picture of them out of the rifle. Drop in is simple, remove the small screw and washer on the top and slide it your milspec lower. DO Not install one in a lower with a flared beyond milspec magwell. You will run into issues with the lower set screws. Reinstall the top screw and washer to tight. The factory ar15 controls are the same with the colt mag, making it a great training tool. LRBHO works the same, the bolt release works the same, and the mag release works the same. The only piece you are adding to your lower is an adapter.

    This is a view of the bottom. The macon on the left and stoner on the right. The macon looks flimsier, because it is. The walls are thinner which allows the magazines to slide free when you release them. This is a key performance factor for pcc competitors. The stoner is not machined as thin and looks beefier, but it barely accepts a magazine. You will also see the location of the lower set screws. These lock the magwell into your lower. The macon locks into the forward aluminum of the reciever, the stoner locks into the triggerguard. The stoner design is stupid, no real way to butter it up. I will be drilling and tapping forward locking set screws.

    At this point of the install tighten the set screws, do not loctite them yet.

    TrSjOKB.jpg


    Top view with magazine inserted. The macon on the left. Center and right are the problematic stoner adapter.

    On the macon the ejector is bent in. This is intentional and part of tuning these to your particular build. These ejectors have some give so they don't gouge your bcg, but to get them to eject properly they should ride the carrier. I've ran thousands through my macon build with it riding the carrier and it hasn't even made a wear mark through the phosphate on the faxon carrier. The stoner is factory set, they are stamped and most seem to curve towards the outside of the rifle, this makes them miss the case entirely. So you will get one case ejecting forward, the next back and then you will get a failure to eject with a live round wedged above the chambered empty. This is an ejector that is not hitting the cases, and the empties are ejecting off of the next to feed.

    The macon ejector was easy to bend into place, the stoner ejector was noticeably harder and more brittle. I will be ordering a spare. I bend mine with parallel smooth jaw pliers (knipex plierwrench) this does not hurt the surface of the metal and leaves a smooth radius at the bend. After bending the ejector in put your bcg in the lower and slide it back and forth into the buffer, the ejector should ride the channel but not dig into it. You can use a snap cap in the carrier to make sure it is in contact when it is supposed to be. Once your happy that the ejector is located properly over the magazine i lightly file the face to true the ejector to the bolt face. This keeps more of the ejector in contact with the spent case making for more positive ejections, it makes a difference.

    Finally i debur the ejector. I radius the top inside edge so that it allows lubrication and does not provide a cutting edge to be in contact with the bcg. I start with a light file then finish polish with 1000 grit. it doesn't have to be perfect, just should not be sharp.

    Another thing you'll notice is the stoner magwell feed ramp catches the magazine follower... grrr... lots of pain to save 50 dollars. We'll fix this in a minute. Test fitting a magazine the magwell is way to tight.

    Y7SJ1EC.jpg


    At this point the Macon armory magwell was ready to go. Loctite the set screws and go have fun. If the mags aren't dropping free but are not stuck in there you can use some valve lapping compound on a magazine and do some insertion and extraction. It will clean it up to the point where the mags fall like a well tuned open pistol.

    The stoner lower is still a pita at this point. Looking at the magazine i can see where the magwell is squeezing the magazines. Time to bust out the files.

    Drop the magwell out. Take out the two screws holding the halves together and disassemble the adapter. 3 locating pins. 1 holds the feed ramp, two hold the bho and the ejector, these have springs that let the ejector ride the carrier without gouging it. I take this as a chance to put a good clean polish on the ejector. I also look where the bluing is worn off of the new magwell from squeezing the magazines. I file all of these points lightly, test fit, repeat until the mag falls free and inserts free. do not go crazy, it's not that much that needs to come off.

    Pop the feed ramp out and hit it with 1000 grit. It doesn't need to be pistol polished, normal use will polish these. the action of an ar 9 is pretty violent compared to your 1911.

    O3rk92R.jpg


    L4FhXtJ.jpg


    Now test fit it back into the lower. Mag should feed and drop free without any issues. I still have a feed ramp that catches the follower and the snap caps. So i carefully filed it back to clear. Light radius with jewlers files and a quick rub of 1000 grit make it look factory.

    H3psfkK.jpg


    Lower is good to go.

    Now test fit the upper without the bolt. You may find it sticks to the upper part of the magazine, preventing it from dropping free or feeding easily. Note where it hits and touch up the upper with a file. There is no mil spec so lots of tuning is required if you want to make a reliable ar9.

    Just a touch of filing, do not go crazy, file -> test fit -> repeat. You can't put material back.

    4KNtTRO.jpg


    Put the bolt in and if it cycles smooth and free with a magazine inserted go have fun.

    If it doesn't... grrr cheap out of spec bcg... My elcheapo bcg in this stoner build (spinta blem bolt) digs deep into the magazine which makes it a nightmare to charge and causes running issues. Im not going to return it, i'm just going to work it in with a spare magazine and some valve lapping compound until it runs right. I would suggest returning the carrier and getting a faxon. tho.

    This is an actual build, and not an assembly. It's fun, but challenging. Use quality files with fine cutting edges. Don't leave tool marks, polish everything. This is how you end up with a competition ready ar9. Or in the case of the stoner build, a ridiculous range toy / meme gun.

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