quote:
First, it is NOT caused by a "lacquer coating" cooking off and leaving its residue in the chamber. If you don't believe me, get a spent shell and hit it with a blowtorch. Nothing's coming off of that sucker. If you've bought your ammo in the past few years, it doesn't even have lacquer on it.

Second, many people believe it is because the steel expands, and, being less flexible than brass, wedges itself in the chamber. That's not true either. But, steel being less flexible that brass does contribute to the problem.

The answer is simpler (and fortunately more correctable) than either of those.

Steel doesn't expand like brass does in the chamber. This allows a slight gap around the cartridge case upon firing. That gap admits powder residue and carbon into the chamber, which begins building up on the sides. Pretty soon, the dimensions of the chamber are too small to allow the casing to move freely in and out. The next time the bolt slams a round into the chamber, it wedges there, unable to be moved without physical intervention.

"Well," you might say, "the 7.62 x 39 rounds that I shoot are steel cased, and they don't have that problem". No, they don't. But, it is not because the blowback of residue into the chamber isn't happening. It is because of the shape of the round itself. The sides of the 7.62 x 39 are tapered enough that they can still overcome friction with the sides of the chamber. The .223 is far straighter, and so it is far more difficult for the extractor to overcome the frictional forces of the now smaller chamber that has a good hold on the straight walls of the shell case.

This post was edited on 6/29/14 at 9:56 pm

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Posted by Shexter

Prairieville

Member since Feb 2014

14016 posts

Posted on 6/29/14 at 9:59 pm to Shexter

quote:
Once, while in the presence of a buddy of mine, I experienced the problem and he said, "You need to run a little brass in every mag to keep it cleaned out."

That didn't make sense to me. How did brass keep the action clean? Besides, common knowledge was that you never mix steel and brass when shooting...that mixing the two would only make this problem worse.

Then I read this article on the Box O' Truth LINK about steel case and brass cased ammo. Although their hypothesis confirmed my friend's statement that brass ammo could help clean the chamber, they stopped short of recommending (or figuring out) that running steel and brass together can make a gun run more reliably.

I figured it was up to me to test it.

I started by cleaning the chamber thoroughly and soaking it down with CLP. I then loaded my mags with one round of brass case for every 9 of steel. Then, I headed to the range.

Fully expecting to get a stoppage before the end of mag number two, the AR kept eating the steel case well past that point. The brass coming out eventually carried a considerable amount of black deposit on the outside of it. It was rock hard and couldn't be scraped off with a fingernail. I did a variety of shooting, including slow firing (shooting once every 20 seconds or so), sustained slow firing (shooting once every five seconds), fast firing (shooting as fast as I could pull the trigger) and even some bump firing (near automatic rates of fire).