The M1 Garand which Americans love to think of as the end-all be-all of battle rifles didn't hold up so well to the sand and surf in the pacific theatre- they usually required a complete strip down and cleaning to get them functioning again, and they didn't work so well in the Korean winter- The M1 needs to be greased to function properly and cold weather froze them up. The M14 wasn't really any improvement over the M1 either other than the larger magazine capacity and better gas system.
Point is, any semiauto is going to fail when its exposed to harsh climates or sand. The AK-47 fares better than most, but you have to give up a lot ofaccuracy, ergonomics, and versatility to downgrade from an AR-15 to a AK.
any combat weapon that sees moderate use ( needing to be fired in the field under combat conditions) that cannot reliably function under those conditions for days without having to be maintained & combine with a poor performance round is a p.o.s. in my book.
Any soldier who cannot maintain his/her rifle to make sure it functions isn't worthy the rifle they are carrying. I'd like to see evidence of the poor performance of the 556 round also.