Nitrate staining from NATO surplus ammo

Short version: Has anyone here ever heard of Nitrate staining of steel, stemming from non-corrosive NATO primers?

Long version: I recently had a PTR-91 rebuilt by a seemingly well-established custom shop (I'm being deliberately vague, as I don't want to make any accusations just yet). However, upon receiving the rifle back, several of the internal components had significant rust. Since the shipping box was damaged, I assumed that moisture must have entered the action. The shop owner agreed over the phone, being emphatic that was no corrosion prior to shipping my rifle. Per his request, I returned it, for a more thorough inspection. He is now claiming that what I see is a purely cosmetic phenomenon, called nitrate staining. This, he states, is caused by residue from non-corrosive NATO primers. There are some used pats in the gun (it's a long story), but at least two of them DID NOT have any corrosion/staining as of 400 rounds ago and three months ago. That being said, many of the last 400 were South Korean and German surplus rounds.
The rifle is being shipped back today, so I will get pictures some more pictures once it arrives.

Some of the South Korean military on the market is corrosive. If it has a K on the casehead better treat it as corrosive which may be. If PS is on the casehead then non corrosive. And some of the OS is also corrosive as well. Some of the Austrian Hirtinberger HP 7.62x51 may or may not be all non corrosive. If boxer primed non corrosive, berdan primed is usually corrosive. Don't remember which German 7.52x51 is non corrosive but there are some lts that are corrosive. if it has the nato cross within a circle should be non corrosive. Frank

Hmm, I'll need to take another look at my headstamps.

Are you saying that corrosive ammunition may have been fired in the gun prior to sending it to the shop?

Because the shop appears to be claiming the rust is caused by NON-corrosive primers.
From the OP "........This, he states, is caused by residue from non-corrosive NATO primers........"

I build my own guns, that way I have only myself to blame.

If you had him blue it, I would say he didn't boil it out fully. When I was helping make 5500 AK 47's US compliant, the guns would come in with many of them growing nitrate/lye fur. It was burning the hell out of everyone's hands, and fingernails were dissolving. The company owner hadn't dealt with it before, so I told him to have someone get some Pepsi from the machine. Cleaned them up with the pop, and the salts were dead.

The fact that none of you are familiar with the term "Nitrate Staining", has me seriously considering that the man pulled it from a particular portion of his anatomy.
The shop owner states that it is a common phenomenon, particularly with roller-delayed HK guns. He is emphatic that it is definitely not rust, and purely cosmetic. The rifle is currently on its' way back to me via UPS, so I'll have a chance to take some pictures.
I have never fired corrosive ammo through this rifle. The corrosion is all over my locking piece and bolt head (for those of you who are familiar with the HK roller-delayed design.) I have not been able to find anything, online or in print, referencing such a phenomenon.
I am more than willing to admit not knowing everything about NATO ammunition, but this doesn't sound right to me.
The rifle had an out-of-battery firing (very nearly lost my hand), and the internals were coated with carbon when I sent it off. During the last cleaning (again, about 400 rounds ago) I took everything down to bare metal, and it was pristine at that time.

Attachment 266408
Okay, I was able to get one that I'd forgotten about. The shop owner actually sent me this picture after I sent the rifle back. This was after scrubbing the spots with a wire brush and CLP formula. There are other parts in worse shape.

I've been engineering around steels for over 50 years, and I've never heard the term either.

Quote:

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Originally Posted by HumptyDumpty

Attachment 266408
Okay, I was able to get one that I'd forgotten about. The shop owner actually sent me this picture after I sent the rifle back. This was after scrubbing the spots with a wire brush and CLP formula. There are other parts in worse shape.

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That attachment doesn’t work for me. Could be my internet connection.

Does not work for me either. I had both the H&K 91 and 93 Shot a lot of Nato 7.62x51 and 5.56 and definitely no signs of corrosion or rusting. I'm really anal about cleaning my firearms and both were cleaned when I got home. My Remington had some LC match through it as well as a Savage 110FP both in 308. Again neither showed any signs of rust or corrosion. Cleaned with
Hoppes then oiled. Heck I've shot LC67 M2 ball in both a Springfield and Garand no problems. Regarding his statement, based on 50 years of shooting, he either doesn't know what he's talking about or blowing smoke. And as far as shooting corrosive ammo, I've shot WWII 303 British in my #4MKII and used plain old water to neutralize the corrosive priming, then cleaned as usual no problems. Bore on that rifle is as when I bought it. Frank

If that was the case wouldnt every military rifle that sits locked up on base corrode. They was good at handing us wore out guns but not corroded wepons maybe my mind is going

Attachment 266428

When I had a 91 I did get some stains on the bolt head but mine was rust, very light though. After cleaning it looked somewhat like yours, from what I recall.

I never used corrosive or 'mildly' corrosive ammo in it. Factory and handloads.

This is my firing pin. What you see was all over my locking piece, along with portions of several other components. At this point, I am forced to conclude that it is rust, and I am at a loss as to why the shop owner would claim otherwise. As if in tacit admission, he bead-blasted my bolt and locking piece prior to shipping it back. However, my trigger pack still looks like this (focus on the side walls).Attachment 266577

Silver nitrate staining is removed with hydrogen peroxide.
I've never heard of nitrate staining from primers, but who knows.

Shop blued over 100K barrels and around 25K firearms and never heard of it.

Quote:

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Originally Posted by HumptyDumpty

The fact that none of you are familiar with the term "Nitrate Staining", has me seriously considering that the man pulled it from a particular portion of his anatomy.
The shop owner states that it is a common phenomenon, particularly with roller-delayed HK guns. He is emphatic that it is definitely not rust, and purely cosmetic. The rifle is currently on its' way back to me via UPS, so I'll have a chance to take some pictures.
I have never fired corrosive ammo through this rifle. The corrosion is all over my locking piece and bolt head (for those of you who are familiar with the HK roller-delayed design.) I have not been able to find anything, online or in print, referencing such a phenomenon.
I am more than willing to admit not knowing everything about NATO ammunition, but this doesn't sound right to me.
The rifle had an out-of-battery firing (very nearly lost my hand), and the internals were coated with carbon when I sent it off. During the last cleaning (again, about 400 rounds ago) I took everything down to bare metal, and it was pristine at that time.

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I am not aware that nitrate staining is "common" with any roller-delayed gun, HK or Zenith who makes fine copies of them. I suspect a cyoa thing going on here as that primer thing smells to high heaven.

And as far as shooting corrosive ammo, I've shot WWII 303 British in my #4MKII and used plain old water to neutralize the corrosive priming,

Ballistol will work on that very well. Make some "moose milk".

Jonp, did a test with some WWII MKVII ball just to see what the velocities were. Ammo had a less than good storage life and many cases were corroded. Managed to find 20 that were free of any visible corrosion. The rest got disassembled saved the bullets and destroyed the powder and popped the primers and sold the brass for scrap. Cleaned the barrel with hot water and checked it for a week after that. Frank