Check some of the prior posts on 5.56mm, particularly LEO. A good soft point, probably bonded. The expensive stuff. FMJ that depends on velocity to cause fragmentation is unlikely to work. I'm guessing you've got less than 2,500fps at the muzzle. If you do meet that threshold, it's barely. And 2,500fps is an average. Anything that reduces your velocity won't work well. You want bullets that expand, not fragment. The good stuff.
Yeah, everything I dug up within the past couple years was for 10.5 and above. Nothing shorter.