"NRM" means "New Roll Mark", when Colt went back to the future and started using smaller slide markings again. Older people like me think it looks bettter. There's also a consensus that Colt also re-committed to higher quality at the same time they changed from the "ORM" (old roll mark) to the NRM, but I'm not qualified enough to know for sure. Try the 1911forum.com for more in-depth analysis.