BudsGunShop.com - difference between 55gr and 62 or 65 grain

Mark, the 55gr is the most common in 5.56 caliber. The only difference is the weight in grains which the more the weight the longer the bullet. All will work in 5.56, it just depends what your targets will be. shootingtimes.com/editorial/ammunition_st223_120606/99587

the Oricle has a 1:9 twist barrel so all 3 should work just fine (up to a 73 Grain) I suggest trying all 3 and going with whichever your individual gun happens to be the most accurate with