Greetings, All!
After spending a week in the Lazy-Boy with a bout of 'La Grippe', I received a reply from RCBS: I was informed that the ".44-40 Cowboy" Sizing Die would likely not change things for me; I was advised to loosen the Lock Ring, raised the Lever Handle on my Press with the Shell Holder installed, and torque the Sizing Die down as far as it will go, resetting the Lock Ring. I did so. With my Remington NMA Conversion beside me, I FL sized fifty R-P cases; these all dropped and fully seated into the six Chambers, and the Cylinder freely rotated all of the Case Heads past the Recoil Shield. I then reloaded them with the Laser-Cast .427-200 bullets, 6.0gr TITE-Group, and CCI #300 caps. Each cartridge was again chambered and rotated past the Recoil Shield ( High primers caused binding in the past! ). I then loaded a second box of cartridges using Star-Line brass; from the second batch, I had ONLY ONE cartridge fail to seat without force, and I believe that this Brass was a dented "range pick-up" case, and I had run it a couple of times through the Expander & Sizer Dies to iron it out prior to reloading...
So, it appears that my dilemma "may" have been solved, although I'd like to shave a little off of the bottom of the FL Sizing Die, if for no other reason than to give myself a little extra leeway when sizing this cartridge for tight chambers.
Lessons learned: 1. MAKE SURE Primers are seated at least flush with the Casehead ( Headspace! ). 2. When working with cartridges that have a SHOULDER, remember to consider headspacing in ALL firearms! The previous FL Sizing Die setting was fine for the Henry and the 1866 "Yellow-Boy" SRC, but the shoulder wasn't being set back far enough for the Remington NMA Conversion chambers. ALL of this should've been "bright flashing lights" to a veteran reloader like me, but...
Again, I think that I'll be giving serious thought to taking a tiny shave off of the bottom off of the FL Sizing Die. I may also see, when the brass case is slipped into the Shell Holder, if I can slip a leaf from a Leaf Gauge between the Shell Holder and the bottom of the Casehead, AND THEN run the Case into the FL Sizing Die.
Hmmm...
M.T.M.