I did a little chrono work the other day, and thought I would share my results.
17 Feb 06
Temp: 68* and sunny
Chrono 10' from muzzle
16" DPMS M4gery
Rem UMC 55gr FMJ 2873 2873 2842 2855 2812 2855 2873 2861
Avg: 2855 SD: 20.7
WCC '86 (Q3131?) 3065 2976 3016 2969 2996
Avg: 3004 SD: 38.5
PMP South African 55gr FMJ 2989 2962 3009 2930 2949
Avg: 2967 SD: 31.4
IMI 5.56 (Q3131 spec?) 2861 2911 2836 2886 2830
Avg: 2864 SD: 34.05
Wolf 62gr Polymer 2704 2704 2699 2635 2699
Avg: 2688 SD: 29.8
***throw out low velocity (2635)***
Avg: 2701 SD: 2.8
WCC Q3131A 55gr 3086 3125 3115 3086 3129
Avg: 3108 SD: 20.8
WCC Q3131 55gr 3115 3122 3108 3079 3065
Avg: 3097 SD: 24.5
Malaysian M193 '84 3137 3182 3167 3174 3212
Avg: 3174 SD: 27
Winchester White Box 45gr HP 3267 3182 3244 3079 3100
Avg: 3174 SD: 83.8 *highest recorded
18" Armalite DCM barrel
Malaysian M193 '84 3236 3212 3226 3220 3252
Avg: 3229 SD: 15.4
Wolf 62gr Polymer 2732 2754 2754 2818 2836
Avg: 2778 SD: 45
WCC '86 3037 3093 3129 3129 3100 3079 3030 3100 3093 3065
Avg: 3085 SD: 33
Winchester White Box 45gr HP 3252 3228 3197 3212 3252 3392 3401 3292
Avg: 3278 SD: 78
Average accuracy was around 2" for just about all the loads. The most accurate load was the Winchester White Box 45gr HP's, which also had the highest standard deviation. The most inaccurate load was the Malaysian M193, which consequently had the highest average muzzle velocity. One interesting note is the Wolf Polymer, which I've chrono'd before and recorded single digit standard deviations in the past. However, accuracy was and still is mediocre.
Another interesting note is the SD's of the ammo stayed fairly consistent between the 16" and 18" barrels, and acuracy was similar in both guns. However, the best group was around 3/4" with the 45gr HP's in the 18" DCM barrel.