As far as You're loads the Ar can be loaded with over a 100gr and I have seen a few 120's bullet weights bullet weight is not so much an issue as the powder, Stay away from ball powders and use flake or perforated powders, as far as how fast you want it to burn depends on how long You're barrel is and were the gas port is located( rifle length, carbine length, Mid?) A good factory bullet that I have very good luck with is federal match, with the 79gr Sierra match king Hollow point boat tail Most of the guns I run it through will cut four or five holes that touch at 200 with good optic and rest. You can get MUCH better than 1.5 with an AR without allot of money going into it by starting with a free floated barrel just floating it 90% of the time in my experience will cut that 1.5 down to a .75 at 100 using factory ammo. Next good sights Metal or glass You're choice, then the trigger. I find the sights to be the hardest part, I like to get the front post out as far as I can Just to make it easier to see, I would stick with the original barrel mounted post sight and attach the sling to the free float tube, then You can Yank on the sling without any noticeable shift in P.O.I. because the FF. is attached the the barrel extension on the receiver and does not touch the barrel. I again really suggest the book I mentioned in my last post for building LR rifles for service rifle, varmint, target, or just getting a good shooter You can really on to shoot extremely well. I You are building a "tactical" rifle You can still expect it to help but in a different application, also goes into reloading theory and covers things that You really need to know for instance the Very low drag bullets (vld's) Molly coated bullets and such which Load COMPLETELY differant than "normal" bullets, Helps You keep You're fingers. IDK if You are going to take it that far though but I still suggest it.