Good question.
Don't have a scale in the house, but fully loaded out with ammo I would estimate the rig weighs in at 25-30 lb. That's with an empty water bladder, so adding roughly 4.5 lb for the 2L of water (2.205lb/liter) we'll call it 30-35lb. Add the weight of a fully loaded shotgun, call it 8.5 lb, and total weight is in the ballpark of 38.5-43.5 lb. The vest and pouches themselves weigh very little. The sides of the vest are open and aside from the areas with MOLLE webbing the rest of the body is lightweight mesh. It's very breathable. For me, the key is weight distribution with the addition of the battle belt. It sits snug around the waist and helps support the weight of the vest. With the weight split between the shoulders and the belt it makes the load surprisingly easy to carry. The belt also carries my 5 In Line pistol mag pouch, a 12 round pouch with extra shotgun slugs, and a med kit.
I have used the rig in its previous configuration during TN summers. Nothing too serious, just a few of us shooting at a buddy's farm. There is a LOT of walking involved to different shooting spots around his land and that was the primary reason I put this rig together. I wanted to be able to carry water, a pistol, a rifle, and a shotgun, plus extra mags and ammunition for all three without having to carry a bag. It does get pretty hot and muggy out there and I do get tired after a full day, but I can tell you this rig is a LOT more comfortable than carrying a big range bag full of guns and ammo. Even a large backpack or my drag bag carried on my back gets uncomfortable after a while, since all the weight is supported by my shoulders. The mesh on the vest makes a big difference and there is another version with even more mesh surface and a built in hydration carrier...