"The answer to that question is bullet selection" Well this is almost correct. The .223Rem will Kill out side of its category/ Class because of 3 Things, The answer to that question is 1.Bullet selection("construction") 2. Bullet placement. and 3.Twist Rate, The latter has a great bearing on just what a given .223Rem can do, with twist rates that Run as Low as 1-14" (mine would make ragged little holes all day with Hornady 53Gr Flat based HP) the now standard 1-12" then there are 1-10" and Many manufactures now make a 1-9" twit this is quite versatile it still seems to shoot light wight pills quite well(unlike My 1-7" Twist) The 1-9" will also shoot most bullets up to 75Gr's At this point and beyond the .223Rem Becomes sort of a Mini 6.5x55mm Swede? particularly when you get to the 1-8" twist and the 80gr Sierra Match King and other similar pills then there's the 90Gr Match bullet as well with twist of 1-7" and even 1-6.5Twist, not to mention its military applications with the Reverse balanced 62Gr SS109 FMJ Pill( steel core at the front and lead at the rear of the bullet ( hence the tight twist of 1-7" for a 62Gr FMJ) as a Note SS109 Pill will shoot just fine from a 1-9" twist But I suspect that it may become Unstable sooner in flight than When shot from the mil: spec: 1-7" Twist? For my all time favourite Goat Hunting rifle and load ( Australian Feral Goats in the Small mountains of the Flinders Range in Southern Australia) I run a Custom Sako L461 with a 23"heavy fluted barrel with a 1-7" and short throat to suit the SS109 but I hunt with a Hand load using the Winchester 64Gr Power Point Pill it is a well constructed Lite skinned Game Projectile with Muzzle velocity that starts out Just under( near enough to ) 3200FPS, This load zeroed just a fraction High at 300Meters allows me to hold dead on the shoulder from 200 to 300M it peaks at about 175+meters so at 100 to 175meters I simply put 3/4's of the goats shoulder on top of my cross hair for a centre hit, this load combo at 250M's with a side on shoulder shot WILL All Ways Break both shoulders and Exit taking the Heart and Lungs with it, With about a 10" kill Zone and a 8X Scope and near to No Recoil this is a very effective tool on said feral goats, failure are only experienced with other brands of bullets never with the Winchester 64 Grain-er as it leaves a exit hole on the far side of about .50Cal ( lets just say that you can well and truly put your finger all the way into the Exit hole) with so many different twist rates ( more than any other calibre) and a good range of bullet weights (35Gr to 90Gr and Iv seen 100 Gr bullets listed for sale "custom ) the .223Rem(5.56NATO) Is Truly a Very Versatile round indeed ( the effective killing ability with the Current FMJ Mil: Spec: pill will Never equal the abilities of appropriate Hunting Soft/Hollow Points when used on Game) 300+ dead Goats can't be wrong? ( 25 in Just one Ambush) Quote of the Day is... The only Good Feral Goat ......... is Meat on the Table. Cheers All, From Aussie Hunter.