[xsrdx]

the 1903 Springfield saw longer service.

The M16 has been the STANDARD ISSUE SERVICE RIFLE longer than any other rifle.

Certainly, there may be incidents of special purpose rifles remaining in service for long periods - M21 and M1C/D sniper rifles, and the aforementioned '03 perhaps - but no other rifle in US history has served for a longer period as the STANDARD ISSUE INDIVIDUAL RIFLE than the M16 series.

[yarddog]

That question got me to thinking about what was the longest serving weapon of any type in the U.S. Army?

At first I thought of the 1911, but the 50 cal. has probably beat it now, at least as far as being as you said, being standard issue.

There are probably some 1911's still being used. I think the 50 caliber dates from around 1920.