Q. I heard that M855 has had serious stopping problems in Afghanistan, and earlier in Somalia. Is this true?
It's possible, yes.
Though early M855 experiments showed the round fragments well in the lab, more recent testing has been showing inconsistent fragmentation. Partially because of the complex construction of the round, M855 has widely-variable yaw performance, often not yawing at all through 7-8" or even 10" of tissue. Testing has shown large batch-to-batch differences in yaw performance even from the same manufacturer, and given the number of plants manufacturing SS-109-type bullets, fragmentation performance is very difficult to predict. This is complicated by the low velocity implicit in using M855 out of the short barreled M4 platform.
Interesting, few of these reports seem to be coming from troops 20" or SAW platforms. It would seem that the additional velocity from the longer barrel provides adequate usable fragmentation range for M855 in the majority of cases. From shorter barrels, such as the M4's 14.5" barrel, M855's fragmentation range varies from as much as 90m to as little as 10m, which frequently isn't enough range.
From Dr. Roberts:
"Combat operations the past few months have again highlighted terminal performance deficiencies with 5.56x45mm 62 gr. M855 FMJ. These problems have primarily been manifested as inadequate incapacitation of enemy forces despite their being hit multiple times by M855 bullets. These failures appear to be associated with the bullets exiting the body of the enemy soldier without yawing or fragmenting. This failure to yaw and fragment can be caused by reduced impact velocities as when fired from short barrel weapons or when the range increases. It can also occur when the bullets pass through only minimal tissue, such as a limb or the chest of a thin, malnourished individual, as the bullet may exit the body before it has a chance to yaw and fragment. In addition, bullets of the SS109/M855 type are manufactured by many countries in numerous production plants. Although all SS109/M855 types must be 62 gr. FMJ bullets constructed with a steel penetrator in the nose, the composition, thickness, and relative weights of the jackets, penetrators, and cores are quite variable, as are the types and position of the cannelures. Because of the significant differences in construction between bullets within the SS109/M855 category, terminal performance is quite variable—with differences noted in yaw, fragmentation, and penetration depths. Luke Haag’s papers in the AFTE Journal (33(1):11-28, Winter 2001) describe this problem."
Opinion: It seems that several projects are in the works to review the use of M855 by the U.S. Military, and even replace the round in light of these terminal performance issues.