AR-15 ?

Idk the 55 gr for me has been the most accurate in the guns I have shot( 1/7 and 1/9 twists). May be my barrel but I can't seem to get mine to hold groups like a 1 in 9 twist shooting 55 gr bullets. Also if you reload you can buy cheaper 55 gr bullets than you can 62 and up. If you shoot 65 gr and up they say you have to have a 1/8 twist or faster. 72 and higher needs a 1/7. Now a buddy shoots some 68 gr out of his 1/9 twist and said they shoot well but know my 1/9 will not stabilize 55 gr bullets well. Sorry if I'm rambling. if your a stickler for accuracy I believe a 223 is great.