Yeah, my first gun was a Mossberg bolt action .410....I used it while deer hunting but never took one with it...lot of squirrels saw the light because of it though.

But yeah....I think it'd be one of the last calibers I'd chose for whitetails....I've seen a lot of .410's over the years, and there's only one I"ve ever seen with a set of rifle sights, and that was the 9410 that Paul spoke of. Slugs+bead front sight=no accuracy past 30 yards.

I'd say let the kid use the .410 for squirrels, and just pick him up a H&R .243 and mounted a fixed 4x scope on it. If you shopped used you could probably get out for less than 300 with the whole package, and it'll be a good, safe, and reliable gun.