I had a partial case head separation using a 1.8oz buffer

[grayfox]

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.

Good piece of info. Thanks. But in the Grendel's case with certain types of brass, looks like that original 556 design can run into problems. Btw my monster 6Arc barrels have the single angle chamfer cut - they seem to be doing great. And my BA barrels, and Uintah. 'Course I don't have any Lapua brass to complete the apparent problem-child "combo".