rust under FSB?

[roar]

How possible is it for rust to develop under a FSB? I noticed some brownish stuff in the edges where the FSB meets with the barrel. I am not sure if it is rust or possibly an adhesive or whatever they use to keep the FSB mounted on the barrel...

It is an LMT upper, which I heard aren't parkerized under the FSB.

[dickfer]

Originally posted by roar
How possible is it for rust to develop under a FSB? I noticed some brownish stuff in the edges where the FSB meets with the barrel. I am not sure if it is rust or possibly an adhesive or whatever they use to keep the FSB mounted on the barrel...

It is an LMT upper, which I heard aren't parkerized under the FSB.

I tend to get that sometimes too, not too bad. Just spray some CLP on a rag and rub it on the bbl and outside of the receiver after cleaning. Not too much just enough to get it on there lightly.

CLP is a rust protectant and should take care of that.

The LMT bbl is not parked under the bbl, I saw this again last week as my FF handguard was being installed.

[roar]

I had been applying CLP on the barrel and receivers, and applied more along those edges after I noticed the brown stuff. I guess I don't care too much, as long as the barrel and firearm continue to function fine, long after I die.

[dickfer]

I jut re read your post. This brown residue could be some gas leakage from the gas block. Not a huge issue if it is not too much leakage.

[roar]

I could definitely be wrong but I would bet that it is indeed rust, and not some gas leak. My carbine cycles perfectly, and the brown stuff makes sense given its location near the unparkerized part of the barrel.

[gasrings]

Gas leakage would be black.

Burnt CLP could look brown. ;)

I pulled the front (non-functional) front sight base off my Bushmaster Dissipator and there was brown surface rust under there. It scrubbed right off. I doubt it would ever structurally compromise the barrel over two or three lifetimes with zero maintenance. Even so, I place a drop of CLP where the barrel meets the front sight every time I clean.

[DJ Niner]

Even the sight frames and barrels that are parkerized in this area will often have portions of the finish scraped off during installation of a tight-fitting front sight frame, so I'm not sure if "parkerized-or-not" is much of a factor in rust prevention.

Same for adding lube to prevent rust; if the barrel ever gets really hot, it will cook the lube and evaporate it. For cleaning rust off the barrel, okay; for preventing future rust, well, I'm not sure how that'll work in the long haul.

YMMV and all that... :)