A lot of debate has gone around on the internet about what the "NM" serial number prefix stands for. Some believe that it stands for "National Match", which is typically the case when you see that marking, however it's not so with Springfield 1911's. It is well known that Springfield Armory Inc. 1911's start from IMBEL forgings from Brazil. The 1911's that have the "Brazil" import marking's on the frame have more than 50% of the work performed by IMBEL, these would have the "N" prefix. The GI's are also made in Brazil and have the WW prefix. The Mil-spec model's can have either a N or NM prefix, with the N being more common.
Springfield's Loaded models, could either have the N or NM prefix. Model's with the N prefix are imported almost complete with the exception of the sight and beavertail grip safety cut's. These cuts are done at Springfield's facility in Geneseo, IL. The NM prefix Loaded's (as well as the Range Officer, TRP and Trophy Match) have the magwell and most of the internal cuts done, but no rail cuts. The final CNC machining on NM prefixes is done in Illinois. This information was from this article.
The rest of the 1911 prefixes such as LW, TGO-2, TGO-3 and EMP all come from Springfield's Illinois facility, though I have seen some older LW's marked "Brazil". The Custom Shop gun prefixes such as CRG, FBI, DEA, and TGO-1, as well as any other Custom Shop marked gun, are also made in Illinois. According to Springfield, the Custom Shop marked guns are built using "National Match" frames.
Is there a difference in build quality? In my opinion/experience...yes. In general the NM marked guns have a better frame/slide fit, than the similar model with a N prefix. Other's on the internet tend to look for the NM marked 1911's as well.Originally Posted by Springfield Inc