Chrono Results (XM193)

I'll be posting chronograph results from various factory and handloaded ammunition as I test them. I chronographed some Federal XM193, which is the 55gr military ball 5.56x45mm NATO ammunition. It is made at the Lake City facility. Chronograph was set up 10 feet from muzzle. It was about 79 degrees outside, with 60% humidity, and the elevation of the area under 100ft. The XM193 was tested in two different AR-15 rifles. The first being a 24" stainless steel Wilson barrel, with a 1-8 twist. The second being a 16" chrome lined chamber and bore Colt barrel, with a 1-7 twist. Both have 5.56 chambers.

The results are as follows:

16" barrel:
Average: 3,249 fps
Standard Deviation: 33

24" barrel:
Average: 3,356 fps
Standard Deviation: 54

Originally I thought that the velocities produced by the 16" barrel were too high. This isn't the case. According to Federal's specification sheet for XM193, the velocity is 3,150 fps 78ft from the muzzle. A little over 25 yards. That's how the military determines velocity.