"does mil surplus brass load the same as factory brass or is there something special that needs to be done?"
GI brass IS factory brass, it's just slightly different from some common commercial types.
There is some difference in the internal volumes between brands but that can easily vary by lots. The only way to tell if the volume is different is to "measure it", and the best way to do that is to weigh an empty case, fill it with water and weigh it again. Compare each brand as you wish and the lighter water weights will be the smallest internal volume.
The volume differences won't be massive so changing brands of brass is not dangerous unless you are loading right on the ragged edge of safety. Few of us do that but, to insure safety, most of us develop a load with a specific lot of components, including brand of case, and shoot that exact load until we want to try something else. Then we start over, going back to a lower charge and only moving up, slowly, if no pressure signs are evident. Following that one rule allows us to safely accomidate a LOT of component variations.
Don't over agonise the crimp thing. It's not critical, especially for a bolt hunting rifle. If you do it, make it look like a factory round.
