Years ago I had a project needing some plastic extrusions. Met with a local guy and got to talking die. They use a pressure extruder, just heating the plastic (ABS) to soft. Used a very short sizing portion with large entrance. IMHO Lee uses a wire extruding shape with 1/4" size section, big entrance with high taper. NOE uses a straight 3/4" size and radii entrance. I'd sure do it different. Too many stuck slick sided rifle bullets i them. Cu wire (pulled) extrude die appear to have large entrance, slight taper then short size section, radii exit. Your approach appears more like a good rifle throat/bore. Only problem I see is we don't use that much pressure, soft alloy will swage to the taper before getting sized. Adds more friction but should, if concentric, make good bullets. Point I'm trying to make that I learned from the plastic guy is the stress and heat generated in sizing causes warping on the exit side. My thinking is the counter bore section needs to be 0.001 over size to prevent bananas. IMHO multical length bullets need a different shape than 'square' ones and I haven't seen any commercial specifically for rifle.