I have tried several different solutions for .40 bulged brass as well:
1) EGW U-Die sizing die (undersized)
2) Redding G-Rx bulge buster die
3) Lee FCD
Here are *my* results (your mileage may differ):
1) The U-die by itself did not do enough on its own, and is very difficult to use without case lube. The cases get stuck in there a lot, even if the brass has been pre-processed by the Redding G-Rx.
2) The Redding G-Rx seems to be the ticket to getting all of the brass to pass the gauge and pass the plunk test for me. I am assuming that the G-Rx is similar to the Lee Bulge Buster, but I am not 100% sure on that. The G-Rx is a pain in the butt to use since each case has to be processed individually, and takes forever. Sort of defeats the purpose of having a progressive press for reloading. NOTE: I shoot a LOT of .40 each year for USPSA.
3) I find that the G-Rx works fine alone without the U-Die, so I have gone back to a standard sizing die, and all is good.
4) I found that the Lee FCD was squashing my coated lead bullets too much, so I went back to a stadard taper crimp die, and this made a huge difference towards improving the accuracy of my coated lead projectiles, and yet the cartridges still passed all the gauge and plunk tests.
My personal conclusions: The Redding G-Rx seems to be the golden ticket for getting 40 cartridges to pass the plunk test, but is a total pain in the butt to use. I absolutely hate it.
The EGW U-Die does not seem to help pass the plunk test, and is very difficult to use on a progressive press, the cases stick a lot.
The Lee FCD over-crimps my coated lead, but with a standard taper crimp die, my cartridges pass the plunk test.
I test 100% of my completed cartridges in the Hundo case gauge.
Like I said, YMMV.