M40's and MIRS rails

im not the most knowledgable about m40's but I have only seen photos of m40a3 with MIRS.

9CCFF667-2002-48E1-A01F-1328505FBBA8_1_105_c.jpeg
275EB28F-D331-4144-B7BD-C725A593CF60_1_105_c.jpeg
125224335_3685049158226304_2034888648813971982_n.jpg
 
The experimentation that most people see took place on M40A3s due to the time period of global conflict, lessons learned, and attempts to make a better rifle for the guys. Also happened with the development of night vision technology. By comparison, the years prior were pretty static. It took the GWOT to breath new life into the development of a lot of things.