I can give you my opinion and the way that I've seen other shooters do.
On bullet weight, many shooters keep seperate magazines for close and long range, they use lighter bullets for short (typically 55 gr.) and heavier bullets for long range (bullet weight depends on shooter preference, distance, and barrel's preference).
The chamber on those barrels are still 5.56. I have heard some issues with reloads and remanufactured ammo in the past with our chambers, but never with factory ammo. I would assume that our chambers hold to the small to middle end of the chamber spec and some sizing dies hold to the middle to large side.
If anyone else has any better info, please post it. I don't have any reloading experience.