PaulBarnard,
An inch and 3/4 will work fine for most deer hunting. In fact I took a very accurate .30-06 on a caribou hunt about 15 years ago--but had to use factory ammo that averaged only 1-1/2 inches for 3-shot groups at 100 yards. The caribou were spooky due to being hunted pretty hard by locals, and I ended up killing both my bulls at over 400 yards, with no problem. Now, caribou are bigger than deer, but in that area not much bigger than mule deer or big whitetails. Their "vital zone" was at least a foot wide, which isn't too tough to hit at 400+ yards even with such "mediocre" accuracy.
