I am not a fan of 243s on deer size game. Yes, they will certainly kill deer and larger animals and do so cleanly every year provided you take care to limit yourself to broadside shots. Having said that, I've seen to many instances of inadequate penetration when anything but a heavy premium bullet is used. In addition, when a big buck shows itself unexpectedly, many hunters lack the judgment to wait for the perfect standing broad side shot. I would suggest 100g nosler partitions, or if your gun will shoot them, barnes X. I don't have personal experiece with the sierra bullet you mention in 243. I have had mixed results with sierra bullets in 308 and 338 diameters (both under and overexpansion). Some people I know who have shot the heavier 243 bullets were dissapointed with the killing performance because they felt they lost some of the explosive bullet performance that kills very quickly on broadside lung shots. The heavier controlled expansin bullets kill very reliably--just not as dramatically as when you turn the lungs into mush with a high velocity varmint bullet. If you shoot light bullets out of a 243 under typical hunting conditions long enough, the day will come when you have a problem. Good luck.