Without trying to irritate anyone by picking on their favorite rifle, it seems like a lot of aspects of the AR's basic design are marginal:
1) The bolt is over stressed for the specified steel. Either a better grade of steel should have been specced, more generous stress relief cuts should have been used, or the locking lugs by the extractor should have been beefed up. Or all three. Alternately, a larger bolt could have been used, which would allow for more steel in the highly stressed areas and better stress relieving features.
2) The cam pin hole in the bolt causes a stress riser. This should have been eliminated. However, with the current design making the cam pin hole in the extractor smaller forces the cam pin to be smaller, which might lead to cam pin breakages.
3) Extraction is marginal. More spring force is needed and/or a widerextractor would provide for more of a margin against failure to extract.
4) Bolt travel is too short. As is, the bolt travels just enough to pick up the next round. Anything that interferes with the bolt's travel results in short stroking. A design that allowed bolt over travel would provide a margin against short stroking.
5) Debris* mitigation features are lacking. The AR has lots of tightly fitted parts with minimal clearance between them. Sand cuts should have been provided like the FAL and/or minimize contact areas of the bolt carrier, and receiver, like the G3, AK, and SCAR designs do. You could even do self clearing features like the Stirling SMG had. A automatic ejection port door like the FNC would be a nice feature too. Anything that relies on the operator is asking for trouble.
The trouble is no one can try and fix any of the problem areas without breaking the modularity/interchangeability of the AR. Design a stronger bolt and you still have to interface with existing barrel extension designs and bolt carriers. Make a better extractor by making it wider and now it doesn't work with the existing fleet of bolts and barrels that are in service.
BSW
*External debris like dust, sand, and mud. I completely agree that carbon fouling in the AR is a total non-issue
1) The bolt is over stressed for the specified steel. Either a better grade of steel should have been specced, more generous stress relief cuts should have been used, or the locking lugs by the extractor should have been beefed up. Or all three. Alternately, a larger bolt could have been used, which would allow for more steel in the highly stressed areas and better stress relieving features.
2) The cam pin hole in the bolt causes a stress riser. This should have been eliminated. However, with the current design making the cam pin hole in the extractor smaller forces the cam pin to be smaller, which might lead to cam pin breakages.
3) Extraction is marginal. More spring force is needed and/or a widerextractor would provide for more of a margin against failure to extract.
4) Bolt travel is too short. As is, the bolt travels just enough to pick up the next round. Anything that interferes with the bolt's travel results in short stroking. A design that allowed bolt over travel would provide a margin against short stroking.
5) Debris* mitigation features are lacking. The AR has lots of tightly fitted parts with minimal clearance between them. Sand cuts should have been provided like the FAL and/or minimize contact areas of the bolt carrier, and receiver, like the G3, AK, and SCAR designs do. You could even do self clearing features like the Stirling SMG had. A automatic ejection port door like the FNC would be a nice feature too. Anything that relies on the operator is asking for trouble.
The trouble is no one can try and fix any of the problem areas without breaking the modularity/interchangeability of the AR. Design a stronger bolt and you still have to interface with existing barrel extension designs and bolt carriers. Make a better extractor by making it wider and now it doesn't work with the existing fleet of bolts and barrels that are in service.
BSW
*External debris like dust, sand, and mud. I completely agree that carbon fouling in the AR is a total non-issue