An American 180 can chew through a bulletproof vest after a few of seconds of fire. A person would either need amazing aim on moving targets, or the target would have to stay still for that to happen, but when you get hit by hundreds of .22 rounds, the deadly factor multiplies exponentially.
Um no. I would have to disagree, the .22 round is a varmit round and it would NEVER pierce body armor even if you held it in one area and kept shooting it. I would give a slim possibility to a .22 magnum round as doing it but not a .22 S-L-LR type of round. They are not armor piercing rounds nor do they have enough muzzle velocity to be effective at anything over 100 yards away.
Muzzle velocity of a .22 LR at 40 grains on the bullet is just 1050 feet/second muzzle velocity. A military .223 round depending on the grain of the bullet (higher grain lower velocity) ranges from 3241 feet second to 2750 feet/second. Now the bullet that I use alot the 7.62x54R (bigger than the AK-47 uses which uses the 7.62x39) in the civilian light ball setup is 2785 feet/second and the civilian heavy ball 2838 feet/second. The military armor piercing round I have which is a steel core 7.62x54R is easily over 3000 feet/second and its a heavy ball (200 Grain) bullet with more grains worth of powder packed into the powder chamber.
But here see for yourself though to the far right is a .22 LR and to the left of that is the .223 round and to the left of that is the AK-47 round 7.62x39 which is shorter than mine and has less powder.
http://upload.wikimedia.org/wikipedia/commons/a/ab/Rifle_cartridge_comparison.jpg
Pretty much what I would have said. Sure, it's not a great round in some respects. It's not like I'm giving you a Lesnar-Style KO with a couple shots, but I'm throwing about 15-30+ per second at you. You might as well be holding up a piece of paper to your chest.
Have you ever shot guns before in real life? Cause honestly a .22 even out of a full auto rifle has a 99.9% chance to bounce off body armor. Ballistics armor cops wear is designed to stop a 9mm pistol round at the very least which is a .38 caliber bullet.
The 9mm pistol I have which uses the 9x18 Makarov round at 92 grains (higher projectile weight than the .22 LR at 40 grains) with a muzzle velocity of 1033 feet/second compared to the ligher .22 at 1050 feet/second. Yes the velocity for the .22 is slightly higher than the .38 (9mm) but because of the heavier round it provides more kinetic energy than a lighter round. So if a vest from the police force can stop a 9mm police round you can bet your ass a .22 would have a very hard time of penetrating the armor. I would probably say it would never happen but I would have to say 99.9% because theres always that 1% fluke where the round hits just right. The military body armor you sure as hell wouldnt penetrate that with a .22 especially on full auto. Those vests we are using in the middle east over there are designed to stop an AK-47 round which has more kinetic energy at longer distances than the .223 because its a heavier projectile than the .223.
Now if both if you want to belive a .22 round being shot full auto can shread body armor thats your choice to but I would have to respectfully disagree. Oh yea I also need to throw this out a full auto .22 wont be as accurate as a .22 semi auto rifle. You would effectively be "spraying and praying" because the rounds wont all travel straight. Ive seen it before at a class III shooting even and got to shoot a guys modified .22 LR rifle to be full auto and I have to say yes it was fun to shoot but those tracer rounds in the magazine were flying all over the place.
Anyways there is a specific requirement for a projectile to pierce armor and the most important thing that allows a projectile to pierce plate armor is the core. .22`s are all soft lead core which would smack the plate armor with a high PING and thats it. Now my steel core 7.62x54R would hit plate armor with a deep PING/THUD sound and punch through leaving a hole 0.35 - 0.40" in diameter.
Now back onto the subject though the .22 light machinegun in game I would say is going to be pretty useless. I know I would laugh and then uninstall the game if the round was able to punch through body armor. I would really laugh and never buy another game in this series if the .22 can punch through power armor.