A while back I went shooting with my AR. Colt barrel, unlined steel. Shot mostly Winchester white box with some Brown Bear in a couple mags. Came home, got busy, put the gun away.

Fast forward several months I got the gun out again and figured it'd be time to clean it up for the spring. Was not at all happy to find rust down the entire length of the bore. I'm talking real brown powdery rust the whole way down. Did I get a batch of corrosive crap ammo or what? My storage is low humidity, I usually only use Hoppes or weaker solvents for cleaning, and none of the other guns in the safe show any signs of corrosion.

I cleaned the hell out of the thing again and I can't see visible damage but I'm not real happy since this was a nearly-unused Colt match target upper from the '00s.

You can just leave an unlined barrel sitting in the safe without any oil in the bore and expect it not to have rust....

At least in this climate you can around here. Usually takes years for uncoated steel to rust. The other guns I shot that day didn't.

I know no one that loads .223 with corrosive primers.

Double post

This, or from everything I hear. There is a possibility you got some off spec powder that had a higher sulfa content but that is a bit of a stretch. An unlined barrel will rust without protection. You didn't take care of your rifle and are paying the piper.

Sorry there really isn't any high probability of a conspiracy.

Corrosive ammo, in my single bad experience with it, doesn't go a fine brown dust type rust.

I shot Russian surplus 5.45X39 through my S&W M&P 15 one day down in NC at a range.  It was kind of misty and damp that day and at the end of the shoot I put the rifle in the case (been in the Blazer all day and was dry) and drove home that Saturday evening.  Got home, ate supper (late) took a shower and went to bed.

Got up the next morning, ate breakfast and my wife went to church and I decided to clean the AR.

HOLY SHIT!!!  I had to do that pull back on the charging handle and bounce the butt on the floor to get the bolt to pull back.  The bolt lugs and lugs in the barrel extension were covered with rust.  I started running hot water through the kitchen sink dish rinsing hose/sprayer and ran hot water through the upper and the barrel and sat is aside.  

I took the bolt apart and the tail of the bolt looked like it had orange fungus growing on it.  Like that orange stuff you see growing on dead wood in trees in the woods.  I dropped the bolt carrier and bolt in the sink of hot water to soak and then sprayed hot water in the lower (the lower looked clean, no visible rust).

I pulled the bolt/carrier out of the sink and took them and the upper out on the deck and grabbed my wife's big heavy duty hair dryer and heated everything up.

Then I noticed the flash suppressor was rusted up, too.  The barrel is chrome lined, so no rust.  Took a brass brush and oil and some rubbing with steel wool to get the flash suppressor cleaned up.  Same for the barrel extension.  Got it cleaned up with oil and 0000 steel wool and lots of rubbing/scraping.

The tail of the bolt was pitted.  Visible pits, in my eyes, pretty deep pits in just 16 hours.

Got the bolt all scraped/cleaned/lubed up and put it back together and then checked it every couple of days for the next week to make sure I hadn't missed anything.

If it's corrosive ammo and the conditions are favorable, it'll rust damn quick.

Don't wait.  Do it (neutralizing the corrosive salts in the weapon) when you stop shooting it.

Every gun I own, rifle, pistol or shotgun, gets an oily patch run down the barrel after cleaning and before it goes back into temporary (or long term) storage.

Good luck with yours.  Hope the rust isn't damaging to the barrel - truth is, a pitted barrel can still shoot good groups.  I've got an Win. M1917 that looks like an old sewer pipe inside and it shoots pretty darn good.  Just takes a lot more effort to get the crud out of the cracks/crevices.

Yes some Brown Bear ammo from Lugansk Ukraine came in back in 2013 or so. It was labeled as non-corrosive but actually was. It was recalled by the importer but they can never get all of it back. Sounds like you got stuck with some of that batch. It was recently sold in bulk with full disclosure a few months ago for a very fair price, but not cheap enough for me to want to deal with the corrosive aspect of it.

WOW! You have to look very hard to find 5.56/.223 ammo that is corrosive. And where did you find a Colt AR with an un-lined, non-chromed barrel?

I think the OP won the lottery of rare-weird unlucky combinations.

I would have no qualms about shooting a few hundred rounds of non-corrosive ammo through a standard, chrome lined AR and not cleaning it for months.  I have done this often without any signs of rust. Assuming it was not in the rain or at the beach. Shooting corrosive ammo through my AK and I could see rust the very next day.

let me guess you mixed this ammo up with the 5.45 primer ammo right?

No, But I did think he was referring to the 7.62x39 Brown Bear offering. I haven't heard anything about .223 having corrosive priming issues, but anything is possible with the Russians. They don't think about quality control and consistency like other European and American ammo companies do.

I've shot Wolf .223 that corroded through the chrome on the FP in less than a few days. Shot it during a class, cleaned the rifle when I got home.

no you didn't because chemistry.

that was a bad FP or something else was messed up.

I have a m16 upper that shoot exclusively corrosive that I don't clean, it has a chromed bcg for a reason. 2nd barrel and probably north of 30k and its never rusted the chrome parts.

i love how mystical corrosive ammo has become for some

the 5.45 primers they make now are not corrosive.

The only corrosive 5.45x39 I know of is the Russian 7N6 that comes in the spam cans.  If you shot that I could understand rust, but Brown Beat shouldn't be corrosive.

Russian 5.45X39.5 ammo should not chamber in a 5.56X45. So I cannot image the OP shooting the wrong caliber in his AR to get corrosive ammo.

I would believe that Tula or Barnaul or whatever maker in Russia used corrosive primers by "accident" for a run of .223 ammo as has been stated. The US and Western Countries have not manufactured corrosive primers since the 50's, before the 5.56 came into existence. But since the Russians had and probably still manufacture corrosive primers for some of their military ammo, it is in the pipeline and could possibly find it's way onto a export .223 production line. I could not find any 5.45 ammo to compare but I suspect that the primer pocket is the same size as their 5.56. But I'm speculating.

What kind of primers are the former Warsaw countries who joined NATO using? They have, or are still in the process of adopting the 5.56.

Several months ago in Massachusetts... so around fall-winter when it was cold/humid outside? And you're saying the unlined barrel was heated up, allowed to cool back down on the ride back, then brought into a warm environment and stored away for months without any maintenance? You've heard of a little thing called condensation, right?

I'm predominantly an AK guy and even though there's some weird mentality about how they don't need maintenance, after every range trip the minimum I'll do is scrub off the bolt face with a toothbrush and run a CLP coated bore snake down the barrel a couple times. 5 minutes work max. I've had light rusting in the gas tube and gas block because of it, but it wasn't a big deal. Knew it was was probably condensation and not the ammo.