Ardent
CGN Ultra frequent flyer
"...with good optics..." Won't make any difference if you use poor quality ammo or ammo that your rifle doesn't shoot well. No scope makes any difference to accuracy. It just lets you see the target better. It will not make a poor shooting rifle or one firing poor ammo shoot better.
"...want a plinker to shoot 12" gongs at 500 yards..." Can you see a 12" gong at 500? Ever shoot any rifle at 500?
500 yards with irons is still easy, on our personal range we have a 12" 500 yard gong and it shows up clear as day though the irons with orange marking paint. Even 1000 yards and irons is no big deal- but you need more rifle than a stock Norc to reliably connect out there. 500 yards really isn't that far, we've shot an SKS to 500 and connected with the gongs once or twice a mag / every 5 rounds or so. I've hit a silhouette at 500 yards with a C96 Mauser pistol too, with witnesses, within one mag. Point is if the OP is happy with hitting the gong every other shot or every third shot, a Norc will likely please him, but he'll need better iron sights, USGI stock would be a good choice. You don't even need super duper ammo at 500 to have fun, again, it's really just not that far yet if you're not trying to win the Match.
Any accomplished marksman can hit a silhouette every time at 500 with a good iron sighted M14. The biggest variable in this entire question is the guy behind the rifle, not the rifle. So while I wouldn't encourage folks to go out and buy Norcs as their long range rifles, he'll have a good time and it'll serve to get him trained up to the point he can make use of a higher quality rifle or build. Good shooting to you.