Die/case float is a tricky thing... Depending on how it floats, and how freely it floats, it can be good, bad, or make no difference. Threaded dies left (slightly) loose in the press can float some, but the threads will force a tilt as the die tries to slide horizontally in the threaded hole. This tilt limits the ability of the die to align with the case correctly. If everything just happens to work out, a loose die can improve the situation, but if not, it may make it worse or make no practical difference.
A traditional shell holder held in a slot in the ram does allow the bottom of the case to slide around a bit. However, if the surfaces are not polished and/or lubricated, the force of advancing the case into the die, together with friction between the case/shell holder/ram prevents the case from freely aligning with the die. Furthermore, most traditional press rams have different tilting forces on them throughout the stroke, which together with necessary clearance in the ram-press bearing, causes the case to advance in a slight vertical arc into the die, rather a straight line.
Comparatively, the Forster Co-Ax allows the die's lock ring, not threads, to float horizontally in the press frame, without the tilt caused by the threads. Then the co-ax's ram and linkage are designed to apply lateral thrust throughout the stroke in only one direction, which takes out the slack in the bearing uniformly throughout the stroke, resulting in the case being advanced in a vertical straight line into the die. Furthermore, the pressure plate underneath the case is polished to better allow the case to slide around when under pressure, and align itself with the die.
Andy
