Re: factory crimp die and coal
As Jim stated, you really don't need to crimp for a Bolt action, however if you are loading these for hunting purposes and the cartridges may see a little rough treatment (like I treat mine) and light crimp is not a bad idea. I'm sure you know what COAL you desire, so don't worry about crimping on the cannelure when seating for your desired COAL.
Regarding the change in OAL, I would suspect the action of the collet is causing this to happen, but I'm not sure on that one. I use the same die, when I crimp I have not noticed this change. I just "kiss" the brass with the Lee crimp die, with no real noticeable markings on the case mouth, a little pressure goes a long way on that die.
hope this helps, and maybe a more knowledgeable re-loader will chime in and have a better answer