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Working on a DPMS LR-308 build and the stripped DPMS lower and upper seem fine as far as fit, finish, quality. I'm still early into the build, so we'll see how everything fits. The only thing I would stay away from are the DPMS uppers which lack an ejection port cover, shell deflector, or forward assist. Also, be careful regarding the rail height for the uppers. The one I have is a low top rail, which aligns perfectly with my Troy quad rail. Not so much for the high top rail uppers from DPMS...
Only problem I had was the hammer pin eventually starting to walk out. Dropped in a retention pin and it's been fine since.
I could be mistaken, but I think the rail height issue with DPMS only applied to the LR-308 uppers and not the AR15 uppers. I had to figure out which height I had for my LR-308 build as well.
I believe DPMS has made both cast lowers and forged lowers over the years. Cast lowers are generally much less desirable - doesn't really matter who the manufacturer is. Only second tier manufacturers ever made cast parts. Those are your Olympic arms, DPMS, Essential Arms, etc. Cast anything is inherently very weak in comparison to a forged part.
Now will that ever be a problem - I don't know to be honest. They were exclusively a civilian version of the receiver. Mil spec calls for a forged 7076-T6 forged aluminum part. Top tier manufacturers use only forged parts. I believe in this day and age all companies now use forged parts - excluding billet receivers. In the case of billet receivers there is often more material added to add the strength missing from not having a forged part. That tells me just about all I need to know on the matter myself. But you may encounter a cast receiver when shopping older rifles - particularly pre-ban models.
You can easily identify a cast lower because the lettering and possibly the company logo will be raised. The serial number is stamped after the fact would would be recessed. I would recommend staying away from cast parts in general. There are too many manufacturers making top quality parts that are very affordable. Even in the pre-ban market there are plenty of forged receivers available. They are at full retard pricing right now, but they are always in the marketplace. Examples would be Colt and Eagle Arms - which frequently appear in the NES classifieds.
So to answer your question on the quality of DPMS - I say: It depends....