Here's some leather armor I'm making for for a guy at the LARP I run. It's not done yet - there are shoulders coming - but it's wearable now (and being unwillingly modeled by my lovely wife, Diana). It's made of HEAVY vegetable tanned leather, over a quarter inch thick. My hands hurt from working with it, but the result is what the game system would consider 4-point reinforced hide armor, essentially equivalent to light plate in the game. It's also adjustable for manly-sized men (I can wear it if I want to, and I'm a big guy, and it goes bigger than that even - I bet it'd fit a 60" chest if it had to) because the buckles on the back are attached with Chicago screws rather than rivets. There are a series of three holes, each three inches apart, for each buckle strap. They can be moved all the way to the edges of the back piece if desired. All the tongue straps are held on with peened copper rivets, so they're super-strong. The lower panels are attached with a floating joint - three in front, two in back. There's no tooling at all, simply because the customer didn't pay for that level of detail.
The strapping is made from 8-10 oz vegetable tanned leather, while the oak leaves and the tassets hanging down off the front are from a tooling belly.
This is some of the more serious armor I've ever made. While my wife had her back turned, I whacked her with half a broomstick. She jumped and was startled (and pissed at me ), but just by the noise - she didn't really feel the hit she said. It's definitely not "costume" armor.