Details at link.http://www.03designgroup.com/technotes/ ... ing-handle
I learned this technique close to a decade ago on an online forum. I don't recall who gave me the information, unfortunately I can't give credit where credit is due. I wrote the following review a few years later because I had gotten so many questions about the purpose of the "red stuff" on my charging handle.
Over the years many guys have asked me what the "red stuff" is in the gap on the charging handles closest to the upper receiver.
If you look at the charging handle on an AR15 from the top of the gun you will notice that there is a half circle shaped gap where the charging handle fits up agains the upper receiver.
If you look at this same area from the side, you will notice that there is a space between the charging handle and the upper receiver. This is where a majority of excess lube, gases, and debris escape out of the upper receiver and are directed into the shooters face.
By filling the half circle gap on the charging handle with RTV silicone you can make a cheap and very effective "gas buster" for your charging handle, and this prevents lube, gases, and debris from being blown back into your face.
Additional tip - THOROUGHLY degrease your charging handle, and use resizing wax on the upper receiver as a release agent.