Mine will allow under hazard loading, which surprised me since my Mausers won't. I had assumed it would not, then accidentally did it one day and figured out it would. Mine is a 223.

I love that little rifle, and so does my 9 year old daughter. She has been shooting deer with it for 3 years now, and hasn't had a single problem with it. She shoots it a bunch. We are already about half way through the barrel on it (3000 rounds or so), and have a replacement barrel on the shelf for when the original goes south.

I think a Grendel would be dandy in that rifle.

I put an adjustable buttplate on my 527 so my daughter could start shooting it when she was 5. She killed her first deer with it when she was 6. IMO, at that age, bullet placement (along with shooting the right bullet) is everything. Having them shoot something they are very comfortable with goes a long ways towards getting the bullet in the right spot. My daughter loves to shoot that little CZ with a can on it and therefore she does go shoot it a lot. 50 rounds in an afternoon, no problem. Since she shoots it a bunch, she can hit exactly where she needs to. Coupled with a good bullet, that means dead deer. She focuses on the deer and the shot, not the rifle. She trusts the rifle, and believes in it. It fits her, and is not too big/long/heavy.

She is 9 now, and still shoots that same rifle. Last week she had to make a pretty technical shot, shooting a doe in the spine over the top of a log that was in the way. It took confidence in the rifle and her own skills, and knowing the bullet was going to go where she wanted it to. She dropped it in its tracks. I have a 243 she can move up into whenever she wants. But I am good with her shooting the 223 as long as she wants to as well, because she is deadly with it. It ain't broke yet, so I'm not going to fix it, if you know what I mean. When she wants to start shooting further, then she will have to step up.

I think you are on the right track. Grendel would be sweet, but a 223 will work just fine too.