If you already have an AR-15 size lower it is a no brainer to go 6.5 Grendel. I have two of them and have killed deer with both. One with 120 Speer Gold Dot and the other 120 Sierra Pro Hunter with handloads. BANG FLOP on both. The 120 Speer Gold Dot is one AWESOME bullet. The Sierra was OK. Even without a muzzle brake device the 6.5 Grendel has virtually no recoil. Put on a brake and it's like a 22lr. BUT, you can honestly shoot WAAAAAAY out there with one. For a light easy handling rifle a 16" or 18" barrel is perfect.
My "adopted" grandson who is 7 years old killed his first deer this year. A BIG doe at 50 yards with a 22-250 55 gr SP Winchester ammo. Perfect heart shot. His real Grandfather who was with him said the deer jumped up mule kicked stumbled about 40 yards and nose dived into the ground. I helped butcher the deer and a 30-06 would have done less damage. Complete pass through but PULPED the vitals and blood shot half the offside shoulder.
My "adopted" grandson who is 7 years old killed his first deer this year. A BIG doe at 50 yards with a 22-250 55 gr SP Winchester ammo. Perfect heart shot. His real Grandfather who was with him said the deer jumped up mule kicked stumbled about 40 yards and nose dived into the ground. I helped butcher the deer and a 30-06 would have done less damage. Complete pass through but PULPED the vitals and blood shot half the offside shoulder.