I have to agreed with emtrescue6 and the others that advised you to reconsider. The kids today are all enamoured with assault type weapons they see in video games. My nephews could not wait to see my AK.

First, that type of rifle is, in my opinion, not good for a young person to learn with or use to hunt. It puts the idea of "there are plenty more shots in there" in their head. A single shot or bolt action teaches patience and proper technique.

Second, while apparently legal in your state, the 223 was designed as a varmit round which, has been bastardized into military service where, it also is out of it's realm. I consider the 243 to be minimal at best for deer. I know, 50 people are going to tell me how many deer they killed with it. I stand by my opinion. You want to build success into your son's experience. He will be so excited that, he probably will not feel the recoil. The more powerful the round, the more "error factor" you are building in your son's favor. That is, if he pulls a shot a bit with a small round, you may have a miserable trailing job or never find the deer. On the contrary, the same mistake with (as an example, not necessarily recommended) with a 444, 450, 280, 30-06 etc., will probably drop the same deer.

While I recommend teaching precision shooting, it is important to build a good experience in as much as possible. Proper technique minimizes flinching. Also, PAST makes shoulder recoil pads which can be worn while shooting or hunting. They come in different thicknesses. I use them when sighting in something which recoils heavily. They make a great deal of difference.

Good luck!