As Ian noted in a prior post it takes time for alloys to fully "cure" or achieve complete crystal growth, hence reaching a reliable size, hardness and toughness. Almost all alloys have this problem, crystal growth is generally near completion once the metal has reached room temperature however not quite,(That's why flash cooling in cold water does what it does) the metal will continue to crystalize for up to a month or longer. Using cryo temperatures this process can be sped up in virtually all alloys, (That we can get our hands on ) and will achieve 99%+ crystal growth around -310 F. Which happens to be just above the boiling point of liquid Nitrogen and that makes it the choice gas to achieve the desired temperatures. A process of ramp and soak cooling is used to lower the temperature of the desired alloy or objects over a period of time until they reach the preset temperature of -310 to -315F, then hold them there for aprox 24hrs, then slowly bring them back up to room temperature. This all varies by the material you are wanting to treat. You have to look at the mass and thermal property's of the alloy so that you do not cool it too fast and stress crack it but to slowly involves wasting gas, which is not real cheap, probably the cost of propane/lb last time I worked with it. The construction of the chamber is not that complicated, I have seen work posted here that takes more talent, your real cost is in the valves and temperature control, Wat-lo was a good mfg when I was in the business. The whole idea is to allow the alloy to cool completely thus allowing complete structural growth, something that can not be done under normal conditions. Something even time will not replicate, it comes close but nothing actually is finished even after a month. Put almost any alloy under a microscope, run a cryo-treatment and look at it again, even if it's already a year old, you will be able to see additional crystal growth, they will be larger and more defined, longer tendrils will increase the "toughness and wear factor" of the alloy. Now does this really make that much difference and is it worth the cost and trouble - No , Is it cool to do? Yes, and It will make your bullets ready to shoot in 48hrs if you really want to do it.