Have you been reading any of my posts? A 310 re-chambered to 32-20 no longer has a 310 chamber, it has a 32-20 chamber. The thicker 32-20 rims are no longer a problem because of the re-chambering. The fired brass is not "Re-formed " in any way upon sizing. It does not become a "tapered case , upon firing, because the tapered 310 chamber is no longer there.
I don't know how to make it any simpler than that...
I've been reading all your posts, and my experiences with projectiles have been very different than yours, but... I have no experience with rechambered Cadets.
My 2 cadets are still chambered for 310, and the chambers are different enough that I need to keep brass and loaded ammo separate. Unmodified 32-20 rims fit on one, but not on the other. Neither fits factory loaded .32-20.
When I tried .312 projectiles some bullets would keyhole at 50 yards. A couple " flyers" didn't even hit the 2'x3' target board.
With .322/.316 heeled projectiles I get sub 2moa at 50 yrs, and my eyes are old.
Here are some specs from new unfired brass
Diameter of Starline 32-20 case right in back of "shoulder"(.820" ) =.341"
Diameter of Bertram .310 case at .820"= .336"
Diameter of 32-20 case right in front of "shoulder" (.950") = .321"
Diameter of 310 case at .950" =.331"
So, at .820" length the 32-20 chamber is .005" larger in diameter,
And at .950" length the 310 chamber is .010" larger in diameter, the 310 tapered chamber would still there after rechambering 310 to 32-20.
I have 2 different makers sets 310 cadet dies, a custom 310 shellholder and RCBS 310 Cadet molds, but I do not full length resize after first firing, I deprime with a 30-06 die, bell the case slightly, seat the bullets with the seating/crimp die screwed all the way out, and use the middle part of the sizing die as a crimp die.
I use cut down fireformed 32-20 brass in one rifle, and cut down fireformed 7.62 X 38 R Nagant in the other, the Nagant ammo works in both.
My best accuracy came with using the softest lead I have to cast bullets, no sizing, and powdercoated (one coat ONLY no matter even if seemingly sporadically coated) Unique powder worked best.
A chamber cast helped me a little to fine tune the case lengths for each rifle using heeled bullets but trial and error woked best. A longer case was more accurate but engraved the rifleing into the bullet, and would stick a bullet in the lands and extracting loaded ammo would pull the bullet off and leave it in the chambeer.
The rifles bore diameters were hard to measure because of the 5 lands/grooves. Calipers end up on a land on one side, and a groove on the other of the slug.