Trigger,
The "bulge" is from rounds being fired from multiple chambers;
Carbide dies can't always size out excessive variances.
A plain steel die sizing cases full length eliminates this in fired brass before the round is loaded, just like full length sizing your 223 ammo.
Please explain the differences between a steel die and a carbide die and why the carbide die doesn't full length size. They aren't the same length?
A steel die returns the case to its nominal unfired size the length of the case and is made with a reamer just like your chamber. Indexing off the shellholder sizes the case full length.
A carbide die is a carbide ring that sizes the case under sized as far down as the ring can contact the case.
Because it is a ring set inside the die it can only index so far down the case. It also should not index off the shell holder or the carbide will break or the retaining ring than holds it may break.
Even if you could index off the shellholder, the ring is set too high to reach the base or pressure ring of the case. Its sizing effect is causing a bulge like squeezing toothpaste to one end of the tube.
This, plus some dies designed for progressive machines sometimes have more bell at the base. Helps with small misalignment in those machines.
I have a selection of size, seat and crimp dies along with different powder through expander funnels for .45acp, there are small differences between makers and even lot/production runs with same maker. I have custom powder through expanders for 9mm and .45acp. Mostly for loading soft lead bullets. The idea is to get the case opened up enough along with bell to keep the case from sizing the soft bullets as they are seated. More stupid bullseye stuff....
