So I've been trying to find another thread to answer this for me but I haven't had any luck with a solid answer. So if I buy a lower marked "multi" for the caliber, can I build an AR 10 on that lower? Will it take the AR 10 magazines? And take the AR 10 complete upper, etc? Or do I need to buy an AR 10 lower receiver? I've built an AR 15 and wanted an AR 10. My LGS has "multi" caliber lowers and I want to know if I can use that for my build. I understand that I LEGALLY can build it with whatever caliber I want, but will it actually work the magazines, upper assembly, etc? Thanks.