As you may notice, the HK magazine spring retention plates are a more elaborate design than that of any other magazine reviewed. That having been said, they are without a doubt the heaviest magazines in the comparison, outweighing the C-Products stainless steel magazines readily.
Speaking of C-Products, it should be noted that the C-Products stainless anti-tilt followers made for stainless steel magazines will fit perfectly into the HK magazines. That having been said, the original HK follower is an excellent anti-tilt device and I have found no advantage which would suggest a reason to replace the HK part with the aftermarket part.
It should be noted that when I tried, the HK magazines did not feed 50 Beowulf rounds due to their larger size. This isn't an issue for most people, as 50 Beowulf is the widest cartridge in common use in the AR-15 platform and it's nowhere near as popular as other calibers.
The finish is a smooth black paint of some sort.
Anecdotal Stories of Military Use
Source: George Hale, US Marine Corps armorer, on 9/12/13: Hey man, I just ran across your analysis of the HK steel magazine in your comparison of STANAG magazines. Im not sure where to add it, so i thought i would let you know. We (in the military circle) seem to have almost universally stopped using the HK mag. Because of its weight, if dropped on the ground, say during reloading drills, it has a tendency of bending the feed lips. However, everyone still loves the P Mag and unfortunately I have had no experience with the SIG mag. Ive seen a lot of soldiers carrying the Promag composite magazines around tho. (editor's note: these are not the same as the promag 10rd STANAG mags reviewed on Gunwiki) But the guys who had it that I managed to talk to about it said they were purchased by their unit. So i dont know if that is a sign of reliability or just the lowest bidder.
Source: US Army Tank driver, 2009 or so: Used HK magazines during deployment in Iraq. Noted that they were heavy; mostly used pmags. Liked the additional capacity of the 40rd versions, however.
On top, we have the follower and to the bottom, we have the two-piece floorplate assembly. The lower left piece has a rubber pad at its bottom end (which keeps it locked in place) and a tab on the top, which fits into a notch on the bottom of the magazine body. The lower-right floorplate piece has three bent tabs towards its center - these are to hook and grip the spring. On the follower, notice the tabs coming in towards the center. These serve to grip the magazine spring and prevent it from separating from the follower. To the left of this, the follower narrows in an hourglass-like fashion. This works with the two stabilizing ribs on the sides of the magazine to prevent the follower from tilting.
Another detail shot of the three pieces. On the follower (top), notice the two tabs towards the center of the follower. These grip the spring and prevent it from separating from the follower. To bottom left, we see the aforementioned rubber tab at the bottom of the picture. Its role is to prevent the floorplate from slipping back and falling out of the bottom of the magazine.
To the right, notice the design of the follower. Were the magazine loaded, bullets would be pointing down.
Inserting the floorplate during reassembly. Note that I am compressing it against the rubber tab mentioned earlier. As it compresses, you get enough clearance to move the metal tab on the opposite side into the notch on the bottom front of the magazine.
The magazine, assembled. The hole in the bottom is to allow sand, water, etc to flow out of the magazine. Not apparent in this photo, is the notch in the forward base of the magazine which the floorplate's tab slides into.
Another picture from a slightly different angle.
Another picture, showing the metal tab on this end of the floorplate assembly.
-- SeanNewton - 09 Jun 2011