Does anybody have any experience with these upper receivers? i am thinking about buying one and haven't really found anything bad about them, just wanted some firsthand experience. i will be suppressing it, and they say their bores are concentric, but has anyone here already done this? they seem like a good buy at around 350 shipped.
http://www.dsarms.com/DSA-ZM4-Forge...300BLK---ZM4CBU300SS/productinfo/ZM4CBU300SS/
http://www.dsarms.com/DSA-ZM4-Forge...300BLK---ZM4CBU300SS/productinfo/ZM4CBU300SS/