OP, A DPMS for $850 used! Keep your money in your pocket and walk away quickly. A new DPMS AP4 IMHO isn't worth 850 new.
To be totally honest I wouldn't cross a city street to pick one up if it were free, unless it had some decent accessories on it!! Pull the good accessories, pull the firing pin, plug the barrel, paint the flash hider safety orange and throw in the kids toy box afterwords. Thats me thats my opinion of their quality. Don't flame, don't post up testimonies this is not a bash. I simply have no use for their products! No one will change or sway this opinion. Oly's are right their also.
Has nothing to do with brand snobbery! But is totally about quality,durability and functionality!