>>64497605
>The M27 is a workaround for replacing the M4 for the Marines
Yes.

>The Marines have long since transitioned to being an amphibious force
Not to the extent that you seem to think.

>and they wanted something that would handle water better than the M4
If this is a stated reason you've read somewhere, it's very retarded, because I can promise you that only a fraction of people in the Marine Core actually do amphibious anything, and those that do don't frequently tend to be in the position where they need the gun to be readied half a second faster. Navy Seals would be those who do amphibious shit the most, and they frequently have other reasons to choose other weapons for that anyway.

>Which is why HK made special modifications to the 416 specifically for the M27, mainly dealing with water drainage after the gun has been completely submerged
Except that you wouldn't really need to do anything further to the 416 on that point. You can drill out a small drain hole in the bottom of the buffertube on a regular AR15 to make water drain out faster, if that's something you really need doing.
The 416's piston doesn't necessitate that, and the thing is so violently overgassed that I don't see why it would need anything further done to deal with water, I'm confident that it can plow through whatever effects there are from that.