Go to Gunbroker or INGO classifieds and get yourself a Plum Crazy Firearms C-15 complete lower. (I just bought one for $119 plus $15 shipping plus $15 transfer) Then you can purchase an upper from same sites or maybe Delton for around $350. Hence, you'll have an awesome AR rifle for around $500 without optics.
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If you're in NWI - go to Blythe's and they had S&W M&P AR-15's on sale for $649
Good luck bro
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If you're in NWI - go to Blythe's and they had S&W M&P AR-15's on sale for $649
Good luck bro