>>63986086
> proprietary upper and lower

If I’m not mistaken. It’s not *really* proprietary. Some years ago, LWRC, in conjunction with Magpul, came out with a non-standard lower receiver and accompanying pmags for the 6.8SPC (picrel). Now Magpul is making pmags for the slightly wider case head of 6mm arc for use in those same receivers. I say it’s not really proprietary because the receiver spec is open source.