I'm having some trouble with the bullets being too loose in the case mouth. Do I just screw the die in further? The some bullets are so loose that the Lee factory crimp die does nothing.

Also I have the crimp die adjust 1/2 turn, should it be more?

Thanks

Brendon, Two things can cause this. Either your case necks are too hard and are springing back or the brass is too thin. If your die is adjusted properly and you size twice (size once then rotate the case and size again) Then look at these things.
You might have to polish the mandril down so the die sizes more. Instructions are on your paperwork that came with the die.
You also might think of annealling the necks.

Polish the mandrel. It is common with the Lee collet die and I bless them for that. Let's you tune your die for YOUR rifle.

Lee also offers undersized mandrels for each cartridge - about $5 a piece. That would leave you with the option of using the standard mandrel on new brass, and the undersized one on older brass, say. In general, it is probably a good idea to work the brass as little as possible - i.e. stay as close to the standard mandrel size as possible and still get a good hold on the bullets. (I know that in BR, people vary their bullet hold according to what their guns prefer, but maybe this is a bit over the top for a .375 H&H??)

That said, I have also experienced that I had to adjust the Collet Die a tad further down, and presto, the problem went away. Doing this, I was careful to follow the instructions that came with the die. I wanted to make sure that I did not adjust the die down too far, and thus ran into a problem setting the shoulder back too far. I have asked this question in here later, and the feedback thus far have indicated that setting the shoulder back is not an issue with the Collet dies. True or not, I'm not sure, so I try to err on the side of caution. The factory instructions leave some room in how far you can turn down the die - notice the difference between using the die in a press that does or does not "toggle over".
- mike