6MM Rem
 

A great factory load is the Federal Premium with a 100 gr. Nosler Partition. Very accurate out of my Model 70 XTR Featherweight. Taken White-tail deer and feral hogs. The partition will drive thru at about any angle without a problem.

If you're going to reload your own any of the 95-100 gr. bullets are suitable for deer. My 10 year old daughter shoots this rifle with the partition load without a problem so your Grandson should do well! Good luck and great hunting.

Should turn out to be a great deer rifle.

I agree, go with a heavier bullet for your deer hunting with this round.

Just another vote with the others that recommend sticking with the heavier bullets...95-110g. While I don't have a 6mm, I have several .243's and they drop deer with 100g Nosler Partition's or Ballistic Tips very effectively. I also have had modest success loading 55g Nosler Ballistic Tips for smaller game. My daughter (7 years old) and my niece (11 years old) both hunt with .243's and do very well with them.