i can only speak about what i've bought and used. 95% of the mb's i have are for AR's in 5.56/223wylde, 243win, 6.5gren, 6.5creed, 260rem, 6.5prc, 6.8spc, 7saum, 300bo and 308win. with the 6.5creen in 22" (if not planning on attaching a suppressor) the lantac dragon and ultradyne 3-port is sufficient. since you don't need gas to cycle the bolt you can get a 5-port to spot/not lose sight of target.