Rock River makes & sells as good as made upper & lower receivers...... John H. of WhiteOak Precision in Illinois, bases his completion rifles on them & he is widely regarded to be the very best AR service rifle gunsmith/match rifle builder in the USA...........Last I knew John was also building M4 clones too on the same..........The prospect of saving $10.00 or $20.00 buying some off brand parts in building a rifle I might need to feed my family, or even to defend them never seemed to make good sense..............
Kreiger, Wilson, & a bunch of others too all make exc. quality barrels............... the caliber, rate of barrel twist & length of your barrel you need is based on what you intend to do with it.
The sliding adjustable stocks are nice & the CAR15/M4 clones are very handy to use getting in & out of vehicles/ buildings & to hunt with.................
hope this helps.
be safe, enjoy life, journey well
da gimp
OFC, Mo. Chapter