The major flaw with their testing is the distance at which the rifles were shot. As stated above the machinegun nests were at least 400 yards away and the bullets had slowed down. The 147gr. 9mm test would lead me to believe that you have to be at least +10ft. underwater to be "safe", once the 8mm had dropped to around a 1000fps it would not shatter on impact. If you are in a boat and jump out and bad guys are shooting at you with rifles at point blank range into the water, then you might be fine at 3 ft. unless someone has a 9mm.