I've made stock many different ways, including IP and regular old pressure cookers. I don't think you get as much collagen extraction as you do with a long simmer (though I'll admit I've never tried 4 hours at pressure like the post above).
Easiest way I've found is to cover the bones with water, bring to a bare simmer, and put the pot in the oven at 220 or so overnight. The last batch I made with venison I actually kept it simmering for nearly 24 hours, and then reduced it after straining. Thickest stock I've ever made by far.
Make sure you have lots of cartilage in the stock bones. The hip joint, knees, ankles, etc are great. Tendons as well. I only cut bones that don't fit in the pot. After a really long cook, the bones will be chalky because so much of the protein has been extracted.
If you want it to be really clear, don't ever let it actually boil, and skim the foam off early and often until you tire of doing it.
My last batch, I put it in a Cambro container to cool in the fridge, and the particles settled to the bottom. Scooped the clear stuff from the top, and used the cloudy stuff in the bottom for chili.
Sadly, I learned the hard way that pressure canning breaks down some of the gelatin, so it isn't as rich after I canned it. It still gels if cooled, but not as much. So, if you want to preserve as much of the gelatin as possible, should probably freeze it. If you don't have a ton of freezer space, though, I highly recommend pressure canning. Stores at room temperature, and it's ready to use immediately when you want it.
