I don't have a Dillon press, but I do use the FCD die--on every round I build in handgun calibers. FWIW, I've probably used it on about 12,000-15,000 rounds in 38 / 357 builds.
Along the way, here's what I have learned about using them.
1. The initial setup is important. The instructions from Lee work, of course, but are really "ballpark" instructions. Precise setup requires one adjust the die body for absolute minimum contact on the case--and that means, really, for the average case length of the batch of cases you are loading. If you're loading well-used cases and have never trimmed them, you may have a wide variance in LOAs that will make for inconsistent crimps.
Once the die body is set "high enough," you can now dial in the amount of crimp very nicely. On revolver cartridges that will produce (Lee's 'modified') roll crimp, but you can vary it from light to heavy with no mashing. On pistol cartridges, the taper crimp will possibly be too light--be sure to use a MAX cart gauge or the specific barrel chamber for ease of chambering.
2. Don't confuse postsize "bumping" with crimping. The postsize "bump" is what you feel when the die first contacts the cartridge assembly; the crimp will feel like a crimp at the end of the downstroke. Postsizing usually is a "double bump" on both strokes. The amount of postsizing seems to be pretty much a function of the bullet diameter (and BHN if it is a lead bullet), assuming your brass has consistent wall thickness, and it may not occur at all.
If you haven't got separate die setups for 38 and 357, I suggest you do that--but it won't stop the need to maybe tweak the die body height at the beginning of a reloading session. I've never trimmed handgun brass, but I do tend to shoot Starline-only, and the brass tends to "stay together" for usage. The mixed 38 Special brass I have may end up being trimmed--but I'll probably just accept the varying crimps on that stuff.
Jim H.
