I think there were 3 different generations of the Ruger RSM. The first generation had the sling band/stud on the forearm and a really heavy barrel.

Does anyone have a list of the serial numbers by model or year of manufacture???

I saw a 375 H&H on-line with a serial number starting with 750-xxxx.

What year of build and model generation, would this rifle be??

Nevermind.

I found it on Ruger's website.

For those interested here is the Serial Number history for the M77 Mark II Magnum Rifle


Beginning
S/Number:.... Years of Production:
750-00205.... 1992
750-00359.... 1993
750-00394.... 1994
750-00616.... 1995
750-00841.... 1996
750-00964.... 1997
750-01124.... 1998
750-02065.... 1999
750-02368.... 2000
750-02791.... 2001
750-03249.... 2002
750-03408.... 2003
750-03633.... 2004
750-04570.... 2005
750-05100.... 2006
750-06606.... 2007
750-07251.... 2008
750-07326.... 2009
750-08020.... 2010

I have a first generation RSM in 416 Rigby. The one with the heavy barrel and front sling stud through the stock. The Serial # starts with 780. Your list shows all RSM serial #'s starting with 750. Had me worried when I first read this post since I just received my Botswana permit for my upcoming hunt. I got the rifle from the safe and was relieved to see it starts with 780.

They do list 780 prefix on the site but it is under the standard Mark II models. Maybe it was the first year.

IIRC, the first generation RSM .416 Rigby came out about 1989-1990.