Excaliber wrote:skub wrote:I had a 5.45x39 upper for my AR, and the only ammo I could find for it was steel cased. After I had shot a magazine or two through it on each range trip, I had pretty frequent problems with FTE. The explanation that I got, which seems reasonable, is that the steel doesn't expand and conform to the chamber like brass does. This leaves room for blowback of residue into the chamber, around the steel case. After a while the residue is sufficient to keep the cartridge from extracting.
The steel case will most assuredly fully expand to meet the chamber walls under the high pressure of the burning powder.
I suspect the problem may be more due to the fact that steel does not have the natural lubricity of brass. This may increases the friction between the chamber and the empty casein some guns enough to produce extraction failures.
A dirty chamber will aggravate this situation further.
That and the lacquer coating on the steel case.