I picked up a number of boxes of ammo that was pretty cheap.  It came in brown 20 rd boxes, labled as PMC, 5.56 mm, Ball M193.  The headstamp says PS @ 12 o'clock.  At 8 o'clock, it says 5.56 and at 4 o'clock is says Oct. 81.  The boxes are lot # PS-E5-726-81        

My question is whether it is corrosive.  I suspect it's made in South Korea and I've heard that some South Korean ammo is corrosive.  I want to run it through my Colt H-BAR and won't if it's corrosive.  I'm only using it for informal target shooting.    

Any help is appreciated.

I've got a couple hundred rounds of this stuff but have never shot any.  I am now curious if I should use it.  I just figured it was good stuff so I was going to save it for a rainy day.

I have never heard of corrosive 5.56.

I had a bunch of that brown box PMC & I wont shoot it again. In my carbine I was getting blown primers & case head flow  back into the bolt face. The firearm was cleaned & send to the gunsmith. He checked the headspace & test fired with the remaining ammo. Same problem, changed brands & no problem. He told me of a Colt that he looked at which wasn't so lucks as mine. PMC ammo again.

NUcadet07 has some pics & if you IM him he may still have them. He also posted pics here awhile back.I will dig out the box that I saved the cases in & post pics if I can.

I bought several hundred rounds of PMC Korean M193 around 1985.  It came in a woodland type camoflauged box of 20 rounds.  It was noncorrosive and just fine for plinking.  No problems at all firing.

1) NOT corrosive.  Not at all.  Nope.  Uh uh.  In other words, it is noncorrosive

2) It's pretty good stuff, though loaded a little on the wimpy side.  It should work great is it's been stored halfway decently.  I just shot the last of my PMC '81 (yes, the same stuff) a week or so ago and it ran fine in my midlength.

There were some lots somewhere of PMC that didn't do well.  This isn't one of them.  VLODPG, I'd be interested in finding out what year your problem ammo was made in, considering that PMC of this vintage was derided for being loaded down, not being hot.

My father and I have put a case of this early 80's vintage stuff through our AR's and Mini 14's with no problem, no jams, etc.  

Howard