Before there was a 445 Supermag I used cut to cylinder length 30-40 Krag brass with rims thinned & reduced in diameter. After fireforming a Lyman 41 mag carbide die has always worked for me. Nothing else needed. My cylinder throats measure .432".
Just checked a few of these & the reduced portion of the case measures between .427 & .430". Thinking the carbide insert is tapered a bit, so maybe just push the case in a tiny bit more to fit your cylinder? There's not enough threads in the press to properly adjust the die for full ram movement, so it's all done by feel. I usually insert the shortened .410 wads before sizing, but can still sneak them in afterward. This sure isn't precision reloading, so if the "neck" is a few thou longer it doesn't matter.
