reforming primer pockets

[Lemonaid]

My gut tells me that a large primer pocket in a brass case with the Grendels base Dia. would be a weak link, but giving 5 rounds a go starting with a real light load would tell the tale...$.02

I think what you would end up with would be like 7.62x39 brass with it's common large primer pocket, sized down to 6.5 Grendel. If the pocket is drilled or milled out to proper diameter in my opinion it would be fine with loads that take into account the extra pressure generated by large vs small primers.