One of the reasons the snake eaters need an oprod gun is that, until you can drain it, it will impair the function of a DI gun if you submerge it and the gas tube fills with water. The OpRod keeps 'em from turning into single shot carbines. Myself, I prevent the problem by slipping a finger cot over the muzzle brake before I go scuba diving with a DI AR.
HK has been hard at work for at least 30 years on cleaner burning powder in conjunction with their caseless ammunition weapons platform. Caseless means there's nothing to eject. But it won't be ready for prime time until they create a case that is so nearly completely consumed that the operating mechanism can slough off what remains with no ill effect.
