Interesting problem
Just brainstorming here,
BigDog(RE) - - - Perhaps there'll be something that will assist you.
As background, I've used Dillon powder measures on a 550B since about 1990, and I currently own five of them, including one i got with a used Square Deal B. I "made do" with only one measure for a couple of years, though, switching it between toolheads. I have used these measures to load Unique powder in .38 Spl, .38 S&W, .380 ACP, 9x19mm, .40 S&W, 10mm, .44 SPL and MAG, .45 ACP, and .45 Colt. I've no idea how many thousands of .45 ACP I've loaded on the 550B, and I guess they've all been with the single, original, powder measure
One problem I experienced had to do with my own "technique" (or lack thereof.
) Using my oldest powder measures, the lids became fairly loose. When I loaded using dirty cases, the powder funnel would sometimes stick in the cases slightly, and it required a lot of force to pull it out. When I jerked it abruptly, the lid would sometimes jar upward slightly. This, combined with an almost-full powder tube and a not-too-solidly-mounted press, would frequently allow the lid to lift and a bit of powder to escape, making a bit of a mess. The problem was aggravated when I was in a hurry, reaching for maximum production speed.
This had little or nothing to do with the design of the powder measure. Cures:
1. Replaced the plywood board on which the press was mounted with a piece of half-inch steel plate.
2. Made it a point to clean my cases, which vastly reduced the binding effect.
3. When using my measures on which the lid didn't fit snugly, I simply put a strip of tape across the lid. Masking, duct, package sealing, cloth surgical adhesive - - Whatever.
4. Smooth operation of the press without a lot of jerking of the handle.
Oh, yes - - Sometimes a primer pocket is not snug enough to hold the primer, and it goes away unnoticed. An unprimed case will indeed spread a bit o' powder around beneath the shell plate. Again, a matter of unsuitable (plumb wore out) cases and not the fault of the measure.
I've used other powder measures over the years - - two RCBS Uniflow, Bonanza, Lyman, Lee, and probably a couple I don't recall. The combination of the Dillon progressive, Unique powder, and quality bullets have enabled me to load truly match grade ammo for years now.
Full disclosure: For the past three years or so, I've been using mostly Win 231 powder for .45 ACP. The majority of these loads have been fired in submachine gun matches. My open bolt Thompson just can't utilize the greater accuracy Unique provides, and I save money with 231.
Best,
Johnny