Quote Originally Posted by Bruce_in_Oz View Post
Then, as the bullet moves up the barrel, the pressure drops enough for the case to "relax" slightly, contract a tiny bit and allow the gas, still at relatively high pressure, to bleed between the case and the flutes, thus starting to "float" the case.
This marvel of engineering relies heavily on the ammunition, (too heavily in my humble opinion). It must be made just right. Any variance can, and often does lead to the case becoming stuck in the chamber. If the case is annealed too much or too little, or not enough area or too much area is annealed, and heaven forbid you use commercial ammunition that’s not made to the exact dimensions demanded by the engineers. And then there’s the type of powder………

H&K’s fluted chambers are notorious for stuck cases. The Sig’s chamber flutes are not as deep, so it’s a bit more tolerant of different ammunition. But the whole fluted chamber concept adds a degree of complexity that’s not necessary and reliability suffers as a result.

A hard extracting, over gassed long stroke piston gun will run like a top on any ammunition. Yes, it’s crude. There’s no fancy over engineering, just brute force extracting the case. But who can argue with the reliability of the AK and PKM? And while not as over gassed the FN MAG, M1icon Garand and the Bren are some of the most reliable guns in the history of warfare.

Some guns are like fancy cars that need high octane fuel or they won’t run right. There’s nothing wrong with cheaper low octane fuel. They are just not made to use it. Putting steel ammo in a Sig or H&K is like putting low octane fuel in a fancy car. If you want burn that stuff, you need something like an F150 pickup that’s designed to run on it.

The Bren was not designed to use steel ammunition, but it operates very much like guns that were and it’s certainly robust enough.