I'll also +1 Springco. Word of advice, stick with the "WHITE Spring" and get a heavier buffer rather than getting heavier springs. Like someone mentioned above, a heavier spring makes the charge handle harder to pull back and I've personally seen one snap and have heard of a few other cases. I don't know what spring was in use or if that was a contributing factor... Point is, the handles can wear out and you mention longevity when maintenance isn't an option so I doubt you would want a spring that could potentially create more wear on another part of your firearm.
That's why I try to leave scenarios or intended uses out of my posts on firearm forums. It becomes fuel for all the self proclaimed experts who rarely offer anything more than vague and relative personal opinions.

