The wall is straight. Reloading the 444 Marlin case necessitates the use of a three-die set. Because the case is tapered, carbide dies cannot be used to reload it. RCBS has been excellent in its service to us. Marlin had been dead for two decades. In that time, no one has tried to sell blank cartridges using this case type.
The answer is yes, you do need to replace the die set when reloading these cases. The problem is that no one makes them and if they did, they would cost hundreds if not thousands of dollars.
The case itself is an improvement over the.45 Colt case because it's thicker at the base and has more material at the top where the primer is located. This gives the cartridge better resistance to blowback when fired from a revolver. The case also has a slightly angled shoulder to make seating into the chamber of a gun easier. However, it's still very difficult to extract loaded cases from some guns due to the angle of the shoulder. Some guns have a pin that goes up through the base of the case and into the barrel stop when the last round is fired. This allows the shooter to remove the spent casing without removing the entire gun from its holster or frame. Other guns have a removable firing pin which can be replaced if it gets bent or broken during reloading.
It performs admirably with older Marlin 795 rifles. It's extremely tough; it doesn't get damaged when it collides with harsh surfaces. It may not completely free fall from your gun. Some users have reported that the magazine does not fully latch. It may be illegal to buy or own in some states; check with your local and state laws for further information.
The firm must receive a notification of fault in materials and/or workmanship within five (5) years of the date of purchase. The warranty does not cover normal wear and tear, abuse, alterations, or repairs not done or approved by The Marlin Firearms Company, or the use of non-Marlin components. Some states may not allow the exclusion of implied warranties, so some might include an additional written warranty from another company. Check your local laws before you buy.
In any case, all Marlin rifles are built to high standards for quality and reliability. When you shoot one, it's clear that quality and design matter to Marlin.