I picked these up because, why not - I could always use more mags for my AR-180.  I'm guessing that these are ~1969-1970 production.  They are 20rd aluminum mags with the "CH" "UI" logo on the front.  They have the metal followers and baseplates are "COLT AR-15" with "CAL. 5.56 MM" markings.  The finish on the two mags is almost completely gone.

They have the AR-180 notch cut in them and it looks to be very well done - arguably even 'cleaner' than my factory original ArmaLite AR180 mags.  However, the rear of the mags behind the feed lips have not been modified, so these may not be the best to use in an AR-180 (I've heard that can cause breakage on AR-180 parts over time).  These are significantly tighter to put into (and remove!) the AR-180 magwell, whereas the OEM ArmaLite AR-180 20rd mags fit in easily and drop free.

Should I finish modifying them for AR-180 use despite the super-tight fit, or are these collectible as they are in some way?  They will work as-is in AR15's of course, so maybe these are best kept as-is for AR15 use...?

Order pictured from left to right is a more recent production NHMTG 20rd mag, ArmaLite AR180 mag, these two Colt mags.

A purist isn't going to appreciate their "dual capability" now, and would only see the "damage/modification" done.
You have 2 mags where the hard part was done, probably got them at a decent price, spend a bit of time and make them work for your rifle and enjoy them.
You can't lower the value on them now, and will only increase their utility to yourself.

It seems that AR mags are a much tighter fit in AR180's than I thought.  Up until I got these, I only put ArmaLite AR-180's mags in it.  Are all converted AR mags super tight in an AR180?  I also tried to put the pictured NHMTG mag in it, and it was also super-tight in the magwell.

I haven't noticed that on mine, a Sterling.
Could it be the notch is just narrow enough compared to the factory that they're hanging on the release, or is it that even starting them in, you are able to see they're tighter?
Try your 180 mags in an AR lower and see if there's a difference.

Mine's a Sterling as well.  It's only got about 50 rounds through it (like new) and is a mid 80's production gun (not sure if any of that matters).

AR mags are tight going in (and coming out) on the AR-180 - not just these two conversion ones.  They get difficult to push in and pull out once the feed lips come into proximity to the magazine catch on the AR-180.  From that point, it takes a good effort to push them all the way in, even if I have the magazine release pressed so that it's not engaging or scraping on that.  I've done that with the bolt locked open as well as closed - no tangible difference.

The ArmaLite AR-180 factory mags won't insert into an AR15 magwell at all.  Tried it in my H&R 601 receiver.  I don't want to try to force them in, as they are pretty valuable mags.

My AR-180 with factory ArmaLite mag:


For the record:  I didn't originally intend for this to turn into a troubleshooting thread for an AR-180 in the Retro AR-15 forum (though I appreciate the help!).  

So, AR mags are tight going in, that would seem to indicate "AR mags are bigger than 180 mags", therefore, 180 mags should slip in and rattle in an AR15 lower. Yet they don't......
The AR180 mag you have is the slick dark purple anodizing, and you said your Sterling is like new.
Got a REALLY used AR mag with like almost no finish? Maybe it's a friction thing, just enough finish is making the mags hang up in your 180?
I'd mic the mags and see if there is a discernible difference.

The AR-15 magazines are tight in the AR-18/180, due to the AR-15 magazine's "over-insertion bump", which is below the magazine catch slot in the AR-15 magazine body. The "bump" is rubbing on the inside left of your AR-180 magazine well.

Attached File

I just tried it. And, my Sterling 30 is tighter than crap in one of my ARs.
Bizarre.

That's right - I forgot about that.  Is the accepted method to just sand that down?  Or cut it?

Good to know it's not just me.  

I've seen AR-15-to-AR-18 modified magazines with the bump sanded/ground flat, and I've also seen them with the bump pressed or hammered flat. Pressing or hammering would require some way of backing up the magazine body internally.

You really want to cut down the back of those mags if youre going to keep using them. That extra length is putting strain on your bolt catch every time you insert one into the gun and that’s what usually ends up breaking them.

I'm familiar with this page on how to modify the mags to work:  https://rifleshooter.com/2019/07/ar-180-magazines-modifying-ar-15-m16-m4-magazines-to-fit-an-ar-180/

But a couple followup questions:

1) The amount that I need to lower the spine of the mag in the rear - is that a critical measurement?  ie, if I go a bit too much beyond, is that a problem?

2) There is some area that needs to be cut from the rear of the follower.  These mags I got have metal followers.  I assume those would be more trouble than they are worth to shave that portion down and I should switch to plastic followers.  Can I use ANY followers for 20rd USGI mags?

3)  There is also a horizontal cut on the rear of the feed lips in the ArmLite AR-180 OEM mag that you can see in my pics.  That isn't referenced in the link above.  What is it for?  Is it necessary?

Nah, I haven’t found it to be critical. More of problem to be too high than a little too low.

However, if you cut the follower too low, it might not lock.



I don’t think you can use anti tilt followers in straight mags. I think they have to be able to tilt toward the end of travel to fully load them.



Not sure why that’s there but I don’t think it’s necessary.

I’ve modded a couple stainless 20s and a few 30s for mine following that blueprint and they all work just fine.

I used a c clamp to flatten out the bump. It works really well on aluminum bodies.

What C-clamp do you have that will fit into the mag far enough to do that?

One I made in shop class 20 years ago

I forgot that it’s definitely a non standard item.

I went with the Nodak Spud replacement lower for the AR180. That saves the original lower and mags from wear.

I converted them back in the ‘80s, still have some for my two 180s. One I did back then locks the bolt back with one still in the magazine - I think I eyeballed that one in a hurry back then! Still feeds well.

How do you hang out here for 14 years, with that many posts, and you haven't bought ONE SINGLE THING here?
Tell me your secret.

I'm guessing he buys things at retail.

Some years ago I had Pete Fleis modify some Colt and Federal Ordinance mags to AR-180 for range use. He had a gig set up for the conversion and also test fitted the mags in an AR-180, all worked fine.