I use a manual powder measure on the turret. Using an "auto" measure (or ANY measure that sits in the "fill" position while the press is operating) will cause variances due to powder settling during operation. Not so much of a problem when loading small charges but noticeable if loading rifle cartridges.
Actually, my experience is exactly OPPOSITE of this. I find that using any powder measure mounted directly on a press while in use causes more CONSISTENT powder throws. The constant vibrations and knocking from rhythmic use reduce variations. This is true with any powder I have used, including fine ball and course flake, and is true with both Lee auto measures and my 1970s era RCBS DuoMeasure. In fact, I believe it is the prime reason I have zero problems getting consistent powder throws with Unique and 700-X. It is also consistent with the instructions that Lee gives with their auto measures that tapping is needed to get consistent throws for small charges with course flake powders.
One caveat, however, is that the powder must be settled after first pouring in the hopper, because the throw weight WILL slightly increase over the first 10 - 20 throws, depending on type of powder being used. I solve this by simply tapping 20-30 times on the measure, then trowing 10 test loads before actually starting production when changing powders.
As for the OPs question about exact weights, I think it has already been answered, but I'll do it again:
If you use any measure that has a fixed cavity size, such as the Lee AutoDisk or Pro AutoDisk, you will not be able to get an exact specific weight unless you get lucky that one of the existing charge disk holes just happens to throw exactly what you want. The charges will be consistently accurate, but if you want exactly 27.3 grains of x powder, you may end up having to settle for something like 26.9 or 27.5. There is an easy mod that some people do to allow you to adjust the exact measure from a disk by simply adding a screw, but I have never found the need for that.
If you really want the ability to throw any exact charge weight from a Lee Auto measure, you have three options:
- Do the screw mod to a disk as needed.
- Buy their adjustable charge bar to replace the disks.
- Just buy the new Auto Drum measure (that is what I would do if I didn't already have several AutoDisk measures that I was happy with).