Just hit'em square in the boiler plate.
In fact, I'm picking up a .243 today. I intend to shoot it but its a present for my ol lady. She's always wanted a "pretty" rifle so I'm getting her one. Really its a present for both of us, cuz I like shooting different rifles for some reason and my other three deer rifles get boring sometimes.
Lots of deer have met their demise at the hands of the .243. A bunch too with .223 and .22-250.
I'll share a story... last year I dropped a doe in her tracks with a 150 gr Hornady SST in 30-06 at about 75 yds. A few minutes later another doe comes by, but even closer and I figure "well I'm going to have to clean one anyway" so I squeeze off a round, but at that instant she catches wind of something and quarters.
What would have been a likely heart lung shot, turned into a lung / liver shot. She falls down and I glass her through the scope. I see her blinking and I sit still. About 5 minutes pass by and I see her lift her head to get up.
Now I think to myself, I better squeeze off another. I do and guess where I hit her? Right through her right eye. I don't mean grazing it, I mean right through the eye (couldn't find an exit wound later but then entry was definitely there). At impact, you could see the little red cloud, if you know what I mean.
I think for sure she's down and done. I wait 10 minutes and am about to go check her. I'm already feeling bad about having to take a second shot... I replay everything in my head and I took a good shot, but sh*t happens sometimes. I mean I've been shooting a long time and never had this happen before.
Well I start getting ready to get up and she picks up her head and staggers up. I'm shocked and mad at myself by this point. Well to make an already long story a little shorter, #3 was the charm, but it was a mental beat down for me. I still feel bad how that doe went. If that last shot would not have worked, I would have had to do the deed by hand, because being a dummy that day, I only walked out of camp carrying four shells.
So whatever you use make it the best shot you can.