Springfield
I also have two 45's , one new in box unfired with the ser #'s are NM###xx. The best answer I can give you is that when Springfield first came out with them they were made in the US, and NM was the prefix given, incidently NM does not signify National Match, later versions were contracted out to Brazil and assembled in the US. Later versions of the Springfields have "Made in Brazil" or 'Imbel" under the grip panels or in the dust cover and come in parkerized finish not blued. Just for comparison sake both mine are 1990's manufacture with blued finish and have five digits after the NM, I also cannot find any Imbel or Made in Brazil markings on mine. I'm not sure that my info is accurate so any other info would be greatly appreciated.