BluntForceTrauma Wrote:GF, what you're calling a "double-angle chamfer" is really just the standard M16/5.56 way of doing it. First they do a 120° cone to help bank an errant bullet tip into the chamber, and then they radius the edges of that cone .0625 where it meets the chamber mouth to round off the edge.
Googled "Sectioned 5.56 Case" and found the attached. Looks like the "web" thickness mates up just fine with the M16 standard feed cone dimensions.
Note also how the difference in web thickness allows the FC case to hold more powder than, for example, the PMC case.
It's interesting that Bill Alexander's quote posted earlier is basically stating that the feed cone should not follow the standard M16 configuration. And it's because of the unsupported wall issue.
To me, the issue is that the literal wider diameter of the grendel case relative to the 223/556 case is structurally weaker (all other things equal) than the higher curvature 223/556 case with smaller diameter. It's similar to how an archway door is structurally stronger than a rectangular door. This could also be why the belt phenomena tends to happen more in the grendel.
Also with more total powder in a grendel round, I'm pretty sure this will put more point force on the brass relative to a 223/556 one.