The DPMS and DSA barrels may not be chrome lined. They state Chrome moly and a couple of the DPMS specs specifically stated no chrome lining. Gotta be careful when doing a search for chrome, if you are looking for chrome lined. Chrome moly just means it isn't a stainless steel barrel, no lining.
Psa has stated before all of their chrome lined barrels hammer forged or not are made by FN so i would go with that as a complete upper and to axxe i did a little research CMT continental machine tool company makes thousands of receivers and parts and are contracted by different firearms companies, colt and psa are some of them.