You need one of these - Rock River Arms AR Varmint 223 Rem/556 NATO 20 Inch Barrel 1/9 Twist Free Float Handguard Upper

I bought this upper last year and tried different types of 55-77 grain factory and some hand loads through it. With most mill spec stuff under an inch @100 y. Good federal/ win 55 g about 3/4 in. Factory black hills 77 match 5/8 in. My 50g v max hand loads are consistent at or under 1/2 in groups. Some in the .2’s.for 5 shots@100.This is the most accurate upper in own. Would buy again without hesitation.