Your shouldnt need any gunsmithing. I suggest buying a book on ARs if you dont know anything about them and you plan to build one from scratch. like the marine corps one so you can under stand how headspace and all that good stuff.
Check them out for matched set uppers and lowers.
http://www.sundevilmfg.com/ there matched set is 319
Check them out for matched set uppers and lowers.
http://www.sundevilmfg.com/ there matched set is 319
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