Some of the best M855 that I have fired was produced by IMI. Here's a short evaluation of that ammuntition.
IMI M855 is loaded with a 62 grain FMJ bullet with a cannelure and has a steel penetrator. The ammunition is charged with "ball powder". The primers are sealed and crimped in placed. The bullet is also crimped in place and the case mouth is sealed with an asphalt sealant. It is easily distinguished from IMI M193 by the green painted bullet tip.
Chronograph data was obtained using an Oehler 35P with "proof screen" technology. All velocities listed are muzzle velocities as calculated from instrumental velocities using Oehler's Ballistic Explorer software program. All strings of fire consisted of 10 shots each.
Accuracy testing was performed using a free-floated 20" Colt HBAR. The barrel has a 1:7" twist, NATO chamber and is chrome lined. Accuracy testing was done from a distance of 100 yards shooting from a bench-rest. A 10-shot control-group was fired using 55 grain Sierra BlitzKings and had an extreme spread of 1.17". Three 10-shot groups of the IMI M855 were fired in a row with the following extreme spreads:
for a 10-shot average of 2.29". The best 10-shot group is pictured below.
The three 10-shot groups were overlayed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for this composite group was 0.69".