I believe those are made by Aeroprecision. So long as its milled in spec (which most are) you are good to go. I don't remember seeing complaints about those lowers.
__________________ Assumption is the mother of all ****ups. Know what you know, Know what you don't know. -Paul Pedzolt "Jack of all trades, master of none, though oftentimes better than master of one" -Mynshul
I've seen lots of build threads (at least a dozen) using those lowers. Never heard of a problem.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek