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Posted: 2/19/2008 1:58:08 PM EDT
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Is this pitting corrosion or erosion, and is it anything to be concerned about? S&W MP15T ~2k rounds fired. Bushmaster bolt is much worse with ~8k rounds fired. 
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Considering that you say the Bushy bolt is worse,I have to ask: What kinda solvent are you using to clean with? And what oil are you using? Being that I doubt there is any corrosive primed 5.56 floating I'd suspect something to to with the above.Especially since you do PM after each use. Hard to tell but there also looks to be some discoloration(blue/yellow ring stain) of the area surrounding the pits as if there has been an acid encountered.Pure speculation on my part,but more info would help. I have not seen the tail of the bolts on my AR's for years as I do not clean the bolt tail completely.I will have to inspect and see what I find as well. QUIB has a pretty effective and proven safe method for cleaning the bolt tails.That maybe something to look at as well. |
I use Breakfree exclusively as it is readily available. I believe the blue tint is a reflection from some nearby object. Any yellow tint is probably from a brass scrapper used to remove carbon. Both rifles function flawlessly. I mainly shoot reloads, 25.0g 2230 and CCI #41 arsenal primers. I am mainly concerned about catastrophic failure that might result in a KABOOM. I suppose a new bolt is cheap insurance. |
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Yeah a new bolt would be ease your mind...but I dont think there is enough damage to the bolt pictured to be of concern. Heck it may have just been a flaw in the surface of the metal. You might contact the manufacturer with a picture of it and see what they say.You might get a new bolt out of the deal. As a side note,I cleaned my Armalite M15A2 bolt due to the fact I have not seen the tails surface in years,and it has no obvious surface damage.That bolt has not had the carbon removed from it in at least 4 years.All Ive done in the past is brushing the area with a nylon cleaning brush and applying FP-10 CLP(using Weapon Shield CLP these days) with a cloth.Otherwise the carbon seems to be self limiting. HTH |
I noticed the pitting on the BM a few months back, just recently on the SW. A local gunsmith said that it was normal wear and tear and not to be concerned. Seeking an informed viewpoint, I posted here. |
Definitely not normal wear. If that was my bolt, I would clean what corrosion I could from the pitting and keep the bolt lubed during storage. As mentioned, the tail of the bolt is not a stressed area, so you should be fine just keeping an eye on the pitting so it doesn’t spread. This is one reason why I stress doing a good PMCS. You just never know where corrosion might form. |
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Soft metal being cut by gas wash? What do the locking lugs look like? CLP should protect steel from the conditions you describe. I'm just wondering if the bolt is out of spec/wasn't heat treated correctly. I wouldn't replace the bolt if the locking lugs look good. BSW |
I removed most of the lube as it is not very photogenic.     |
It's a good start, but if it swallows the gage it doesn't mean that the bolt is bad. You need a 5.56 NATO field gage. Check your hometown forum for somebody that can lend you one. BSW |
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I have an M&P 15T as well and while cleaning it this morning I noticed significantly more pitting on my bolt than your pictures suggest, in the same location too. I constantly run into feeding issues, usually a failure to fully extract a spent case and an attempt to re chamber a new round resulting in a double feed. Have you had this sort of problem at all? I replaced the extractor and that helped. The gun is used so I don't know how many rounds went through it before me or how it was maintained. HELP ME!!! |
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Try here: Library\Technical Notes Look for: TECH NOTE 50: The Cycle of Operations as a Guide to Troubleshooting TECH NOTE 32: Identification and Correction of Malfunctions |
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