Where do you buy the weights?
And, isn't an H3 5.4 OZ, and the heavy AR-15 Odin 5.8 oz?
Midwest tungsten service is one of many places that sells them.
There's no possible way for an ar-15 buffer manufactured to proper spec with one tungsten weight to weigh that much. If you're getting away from the proper spec, then of course anything is possible. But then that means that....ANYTHING is possible (in terms of things not working properly). If an H3 and stiffer spring are installed and the rifle is still overgassed (assuming it's a small frame platform rifle, PCC and large frame are a different issue) you need adjustable gas at that point.....or you need to buy a barrel from someone who knows what size a gas port needs to be, and where.
For those desiring a lighter-recoiling rifle who plan on using adjustable gas and a tuned load, it's a fantastic idea.
Definitely not ideal for those desiring a heavier buffer.