as much as i'm proficient on the handling, firing and repairing on my m4's, i am a little lost on the gas operated system on the H&K MR556/416... from what i've seen, these rifles are super reliable, rarely need to be cleaned, and don't have the same blowback issues that the m4 is so well known for.. i just saw the video of the comparison between the H&K 416 vs the colt m4, and i must say i was impressed... so here's the questions i need answered.... first off, can these rifles really be shot after being submersed in water? secondly, the price tag for the civilian version up here in Canada is about 3700k U.S. dollars and im curious if this is an outrageous price or a fair buy. lastly, are the gas operated system on the MR556 the same as the Sig 516? if so, is the Sig a better buy?

thanks in advance for the help