Bullets from weapons in the ME universe aren't likely to be stopped by any kind of armor
Why is that? Armor always keeps up with the latest weapon technology. When they invented shaped charges that would plow through a meter of hardened armor steel everybody thought that tanks would be easily stopped and and obsolete now as it defeated the conventional armor SO hard.
And then they invented reactive armor that works fine and tanks are still rolling around on the battlefields.... And now they're already working on defensive systems that shoot RPG's and any other kind of projectile mid flight before they can even touch their armor.
Also, the weapons in ME shoot tiny projectiles at VERY high speeds, but that's nothing special, the ISS space station has to deal with this kind of problem on a daily basis. Its called micro-meteorites, tiny rocks that move several times the speed of rifle bullets. The irony is, those are easier to stop than conventional bullets despite them having several times the energy. The ISS has two simple metal layers, separated by a couple centimeters, the first layer gets punctured easily but the tiny meteorite breaks part in the process because of the immense impact speed and the energy converted into heat ( a LOT of heat) , the second plate easily stops the remains that is now dust.
The projectiles in the mass Effect universe would actually be laughably easy to stop even if they were made of tungsten, despite their awesome energy and speed. Of course, game play wise that would not work but Bioware developers are clearly no weapons experts.-