I've got a 4000 sqft house to trim. Nice big casing, 1 1/4 x 5. These casings have plenty of meat for biscuits or big pocket screws. For the last 5 years my trim carpenter friend has been using big screws from the head casing across the miter. He thinks they hold better on the big casings versus the biscuits. You don't get the teeth marks from miter clamps as well. Anybody using big screws instead of biscuits?
(Cabinet and Millwork Installation Forum)
From contributor B:
The part of the miter that usually opens is the inside. That is hard to hold with screws. The biscuit should be placed as close to the inside (short point) of the miter as possible. On a 5" casing I would use two. As far as the miter clamps, back out the middle two screws on both jaws. Now you will only have two small holes on the edge of the casing. You will already have 20 + nail holes to fill on the face of the casing. Nothing pulls the joint together like the miter clamps.
We always laugh at the newbies that come to town selling big casings by saying it is all "just one piece - half the labor." Then the builder buys a bunch and the carpenters do their best, but all the miters open 1 to 6 months down the road.