Congratulations to your nephew. I am retired LEO myself.
I believe Fulton uses a cast receiver if that makes a difference.
Look also at the new Rock Ola M1carbine by James River Armory. Best to Google it for reviews. Receiver machined from 8620 billet steel. Seems to be good quality also.
For me an excellent condition USGI carbine would be my first choice. Not hard to find. Plenty of people here and other forums to walk you through what to look for and what to check.
Whatever carbine is chosen use magazines of know quality. These would be new USGI magazines, with 15 round mags having the best reliability. The Korean mags marked "UU" have a good reputation also. I would avoid all other commercial magazines. Using soft point ammunition? Insure the carbine feeds these with no issue. Most do, some don't.
Take care, and tell your nephew the same.