How did the Bundeswehr keep steel mags from rusting? I had some MP5 mags in a mag carrier that got wet and started to show some rust spots. The mags were lightly oiled previously (or I think they would have been completely orange) but how did they keep mags from rusting in the field, or was this just something of little concern as they’re a consumable? All my experience is with aluminum mags, or polymer. Never been in the field with steel mags.

You have to piss on them.  It works. Trust me.

got a few of them-I think they have some sort of Teflon style coating on them. Don't have an HK to compare but I don't expect any problems

The same way GIs did in ww2 kor and VN, they cleaned them all the time.

That’s what I was thinking. Got to be a pain in the ass in field conditions. I guess being pretty much born in the aluminum/polymer era I’m spoiled.

Wax or grease. Hornaday one shot works great.

Some well-applied RIG grease would not go amiss.

Keeping them away from Louisiana is also a good plan.
My HK ones are all hot caustic blued, and rust easily. I have more of the old KCI mags, which are zinc phosphate coated (better).

Loved the food and the people, didn't care much for the climate when I was there, too much like Houston.
I was thinking about having a coating or different finish applied, but I don't know if I want to go that route. But finding small orange spots on my mags after being around rain (not even in actual rain) raised some concerns. I just ordered some of the spray lube suggested above to try out, figure it will be good for inside the mag tubes as well.
Last Friday I had a frantic hour downloading, disassembling, cleaning up, lubing, reassembling, and reloading 6 MP5 mags that got wet after we got several inches of rain in the area. I typically wipe the mags down after each range or cleaning session with some CLP but apparently that was insufficient.

CLP evaporates within a week or so and, contrary to popular belief, has little/no lasting preservative effects.

I really like RIG and it is common/inexpensive.

I cringe when I see those older pics of SEAL's coming out of the ocean with MP5's even though most of them are rubber ducks.   They must have some cleaning regimen for them or they would be trashed.

When I lived in East Texas my local dealer was a big time NFA guy. Allegedly, there was a PD SWAT team that had gotten a full load out of HK weapons: MP5s, PSG, USP, Benellis, everything. They went to a shooting school and at the end, one of the guys had claimed to have been a SEAL and told them about how they cleaned weapons in Vietnam by taking them into the shower. So they did just that, and then stowed their weapons in Pelicans and drove or flew them home. On returning and opening their cases, (again allegedly) they had a nice set of orange HKs.
No idea how accurate this was.

That sounds pretty accurate.
lol

They would've needed to dry the parts prior to lubrication and reassembly.

The problem with MP5s (and all the legacy RDB HKs really) is there are impossible-to-reach areas inside the sheet metal receiver (like around the trunion) where displacing the water is extremely difficult.

If I knew I'd be going swimming with one, I'd strive to get all those places completely filled with grease, so the water couldn't get there in the first place, and upon return... after soaking in (hot) fresh water, use WD-40 to displace any residual water, followed by a meticulously thorough cleaning, with weekly inspections for the next few months.

A solvent tank (parts washer) bath would be even better.

It's my understanding that outside of propaganda/recruitment media, SEALs utilize tough, buoyancy-compensating, waterproof "dry bags" for their weapons, and the only ones which may actually get exposed to seawater would be those of the team's scout/swimmer pair (that conducts the initial surf zone recon), but I'm going to theorize that even they tend to use bags and avoid opening them whenever possible. I don't believe OTB insertions are anywhere near as common as TV would have us believe, and they tend to do aerial or vehicular insertions on most ops.

MP-5's weren't general issue to the BW.....

They went to the Federal Police, BGS, and special forces.....

Carried a little....shot even less, and cleaned a lot.....

There was a recent book by one of the more prominent/well-known/publicized SEALs that mentioned having a heavy plastic bag that basically had a built-in glove for firing in a wet environment. I can't remember who it was, might have been the guy that wrote the Bin Laden book or maybe the 5.11 guy.