Re: how to connect prefinished cornw moulding
with prefinished material i always cut off the last couple inches off the end no mater what. if dealing with mdf the factory ends are always ragged and swelled up from absorbing the primer and paint. by cutting it you'll have a truer piece to join your next piece to.
i dont like fitting two pieces on the ground when it comes to crown, with the two planes of the ceiling and the wall they arent always dead straight, so having a good joint on the ground is one thing but once its up at the ceiling any imperfections in the wall or celing can throw off the joint. Also you should use a scarf joint, bevelling both pieces so one overlaps the other. i use either 22 1/2 or 30 degrees, its less susceptible to shrinking like a 45 deg scarf is
as for pocket hole screws or biscuits, both will work but the material has to be 3/4 " stock
fire up the saw and make some dust