The only dedicated 5.45mm AR-15 magazines that I know of are the C-Products/ASC/Stoner 5.45mm mags. Except for cosmetic batch-to-batch changes, they all seem to be more or less the same. Finishes vary from a sort of matte grey, like the Fusil AR mags that I have, to a glossy black. The followers, springs, and stainless magazine bodies all seem to be essentially identical in form.
The finish on the magazines, by the way, kind of sucks. After a few uses, you’ll notice that the finish is wearing off, maybe flaking off, around the edges, especially where the mag fits into the rifle.
Although, I’ve heard that some shooters are having better luck with the new ASC (Ammuntion Storage Components) magazines, the three that I bought from AIM Surplus all gave me the same problems that I had with the C-Products magazines. C-Products closed down shop, but rumor has it that ASC is the same people, making the same parts, off the same tooling and machinery. The product line is essentially identical.
The Stoner magazines from Midway are rebranded C-Products/ASC magazines. There may be some 5.45mm AR-15 magazines with Smith & Wesson stamped on the floorplates, for the M&P15R rifles and uppers – same deal as with the Stoner mags, rebranded C-Products/ASC.
The C-Products 5.45mm followers are similar to a no-tilt follower, but with no anti-tilt leg at the front.
There may be some magazines out on the used market with skeletonized white plastic followers. There was a guy selling these followers on a few gun-related message board classifieds as improved. 5.45mm AR-15 followers. Last I heard, Spike’s Tactical had the tooling to produce these “improved” followers. At least one batch of Spike’s 5.45mm uppers came with a magazine with the white follower already installed. They had stopped this by the time I bought my Spike’s upper.
I’ve read that the “improved” followers only work with the earlier C-Products magazines. I can’t confirm this because I can’t get hold of one of the followers, and besides that, all my magazines seem to be structurally identical.
The ASC magazines that I fixed the feedlips of are working well with the black 5.45mm followers that came with them. I had originally tried the Magpul follower because I didn't know why the magazines were giving me trouble. I tried it again when I found one magazine that just refused to work, and I was getting desperate. Not a necessity, but if you want a high-visibility follower, or if it's something you think might help, then maybe it's worth a try.
Springs for standard AR-15 magazines will not fit the 5.45mm bodies. The 5.56mm AR-15 magazine springs are too wide to fit the 5.45mm bodies. AK-74 magazine springs will fit, but nobody sells just the springs. You’d have to scrap an AK-74 magazine to get the spring, and they aren’t that cheap at $13+ each for surplus magazine. AK-47 magazine springs will not fit either. (EDIT, no longer true, scroll down for note on Wolff magazine springs)
The C-Products 5.45mm magazines are, unfortunately, a little bit on the short side, and don't have enough power to trip my extended bolt catch consistently. You may even have trouble getting them to feed reliably without spraying some dry lube into the magazine tube, because the spring has a hard time pushing up the ammo fast enough before the bolt carrier returns forward.
Width and length of the 5.45mm AR-15 magazines are standard G.I. size, so they’ll fit most any mag pouch that will work for a 5.56mm AR/M-16 mag.
The LULA AR-15 magazine loaders don't work with the 5.45mm magazines. The Pro-Mag loader that crams 5 rounds at a time into the magazine at once, and works well with 5.45mm magazine, as well as with 5.56mm mags. I got my Pro-Mag loader from Bravo Company USA (they call it "AR15 Personal Magazine Loader 5.56mm"), but they are available from other places too.
Magpul Ranger plates will fit the 5.45mm magazines, but again will require modifications. Just for kicks, I spent maybe 10 minutes cutting the lockplate with a hacksaw and round file. I don't have any of the Magpul L-Plates, but I would imagine they would work with the same modification.
PMags with 5.45mm ammo
With the front leg of a new Magpul PMag Maglevel follower cut off, 5.45mm rounds will feed well, and the magazine holds 29 rounds of 5.45mm. The mag, modified like this will not trip my extended bolt catch when it runs empty though. The LULA 5.56mm AR-15 loader sort of works with the modified Maglevel, but not as well as with 5.56mm ammo.
The older Maglevel magazines without the dust cover that clips onto the bottom, or round count markings, will jam up when you try to load them with 5.45mm ammo, even with a modified follower.
Related Link: Desecration of a PMAG: 5.45x39mm - Cutting the follower, and magazine compatibility.
Other Magazines with 5.45mm ammo
I'll spare you going through all the different kinds of magazines I have individually. D&H aluminum with Magpul follower, standard 30-round PMags with no window, PMag 20s, and 30-round Troy Battle mags will generally work okay if you don’t load more than 12 or 15 rounds. If you try to cram in more than 15 rounds, the ammo or the followers will jam in the tube, and the magazine won’t feed properly.
I tried a 30-round Lancer L5 magazine, but it jammed up when loaded with 12-15 rounds. The magazine body bowed out, making it difficult to insert into the rifle, and it definitely didn’t drop free when the mag catch button was pressed. I believe that there are multiple generations of the L5 magazines. There are reports of some working better than others.
EDIT: 9/28/2014 - Extra Power Magazine Springs
Wolff Gun Springs has started selling AK-74 magazine springs. They are longer than you need, but I think they have fixed my problem child magazines. At $5.60 each (when you buy 10) they are a little expensive though.
I cut off 5 coils, and bent the end of the spring to hook onto the 5.45mm AR follower. Not really a big deal. You could probably cut off more, but I figure that it's easier to cut off more later, than to try and add coils back on. I intend to buy more and replace the springs in all of my 5.45mm AR magazines.
M4Carbine.net Forum: I am taking the 5.45x39mm plunge - currently at 57 pages
AIM Surplus: Spike's Tactical 5.45x39mm 16" Mid-Length Upper
AIM Surplus: Spike's Tactical 5.45x39mm 8.25" Upper
This article is an attempt to compile all the knowledge of the 57 pages of the M4Carbine.net thread, other sources, and my own personal experiences. Thanks to Neckbreaker for finding the PMag modification thread on XDTalk. Thanks to thisguy41487 for having the balls to hack up PMags. Thanks to whoever figured out the Magpul follower mod - I can't find the thread, or your username, sorry.