Whats the best ammo for killing racoons with my 20" 1/7 twist AR?

Assuming you mean racoon, I would go with a 50-55 grain hollowpoint load.
If you need total bullet destruction, go down to 45 grain, but you will lose some reliability in penetration.
Raccoons are a little big for a 40-45 grainer, generally.

Im sorry, I didnt think, I should have not said coon, yes I mean racoons, those fuzzy cute little bastages that are nesting in my barn.

I killed four of them last year with a .22 pellot gun outside my apartment building.

The coons get into the dumpsters almost every night. They come right up to the screen doors and there are a lot of kids arround so I waited in the parking lot, with the gun in the car until they came back. Every night I thined out their ranks until they stoped coming back.(or I killed them all?)

If you place your shots, anything will work. The best for hunting would be a HP or SP, for coon I would just use whatever you have.

I would use a .22 pellot gun or .22LR with subsonic ammo (and don't miss) to limit collateral damage to the building. I guess you don't want holes in your walls right?

I was thinking what Justlooking said.  I would think that any well placed round from an AR would work on a raccoon sized animal.  No expert, but just my thoughts.

.22lr works fine on racoons (hmm I have always referred to them as coons, I think it is still PC to refer to them as such as long as you are not from the south).  FMJ in .223 will definitely do the job if you just want to kill them, however, it will make a mess of things.  If you are saving the pelts, I would recommend .22lr instead.

Don't forget your ears..
Watch for fire if you're around hay or straw.

The skunks, coons, and possums ate me out of cat food on a regular basis until I moved it from the shed to the patio.  

Started out with a 22lr pistol, then 22lr rifle, and settled on a 22 mag marlin.

Tried various 22 ammo of the hot variety and it all worked if you could get the good head shot.
Ifound it didn't always anchor them on the spot if my aim was off or I had to take a body shot.  

Went to the 22 mag with the Winchester 30 or 34 grain hp.  Anchors them on the spot with a decent hit.

Just open upstairs bedroom window and take the shot.  Tell dog, good job.  Then go back to bed.

CB's and a 20-24" bolt gun... real quiet, hit right, they'll drop.

Any round will work for a 'coon, but a coon ass will shoot back!!

If you plan to shoot them inside the barn, then use a very fragile varmit bullet. Like the little 40Gn Vmax.

I've killed plenty of michigan raccoons. a Bull can bget as big as 45pounds. a 22LR really isnt enought gun for human kills.

BTW; Racoons are the number 1 rabies carrier in Michigan. They also carry other diseases than can be passed on to humans. Handle the dead coon like HAZMAT.

I recently killed the biggest raccoon I've ever shot... A male, out in the middle of the day, sitting next to my pile of split hardwood... He had no interest in leaving when I approached, instead he just sat there, hissed and snarled...

I figure RABIES or something nasty, the first shot from the .22LR doesn't catch him solid in the head and the games begin... Took 7 more rounds to finally finish it... wrong gun, wrong round, pissy first shot... He was an easy 30-35 pounds and buried on the spot.  I thought of having him tested but had no interest in handling the damn thing...

Either use more gun or shoot better than I did.  All that .22LR did was make him really mad... [;)]


edited to add:  I had the proper gun with me, my 'beater' AR loaded with Federal AE 55gr, ofcourse it was in the truck... Now I carry it and leave the 10/22 in the truck...