Have used 223 for several years Have had 21 one shot kill[8D] and one three shot[:@] Last year two with one shot[8D] Use Hornady 50 gr. SSST and Barns 50 gr X Bullets.
The secret is knoww your gun, and how it shoots and where it shoots with each shot after a good cleaning.
My longest shot was 280 yards, with only a 3 inch drop.
The best thing is I have a whole deer with little or no wast[:'(] Can't say that with the 7mm mag.