RE: Will a .243 "drop" a deer quickly?
A .243 will drop a doe right in her tracks.
A .243 will drop a small 4 point fork-horn right in his tracks.
A .243 will even drop a nice 6 pointer.
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But a .243 might drop a 250 lb monster 10 pointer where he stood, you'd just have to be real accurate with your shot.