Never heard of a 'button die'.
If you're talking about sizing buttons, this is common expansion/decapping with sizing dies -whether FL or bushing.
But I follow a contention that pre-expansion is important, and it's important for even more than driving thickness variances outward(away from bullet seating).
Pre-expansion can also reduce excess seating forces which greatly helps in precision seating. You do not want to use bullets to upsize necks.
There is another attribute to manage for those making/storing ammo for future use(not immediate).
When we size brass we add energy to it and cause yielding. That energy wants to go to a lowest state, and continues if it can to do so over time(like memory). Given this, last sizing action is countered with spring back that continues over time but never fully reaching original state(due to grain structure change). This is true of any brass hoop sized anywhere, provided the energy has not be removed (through full annealing).
When you downsize in a die and then remove that die the brass springs back counter to this action(outward). If left to it's own, over time it will continue to spring back outward. When you expand brass, it counters inward.
I have to throw in here that any dimensional change that is not yet causing yielding is not sizing, and not adding energy.
Anyway, where we blindly follow the 2thou under loaded OD rule for bushings there can be occasions where we're actually sizing down 2thou under loaded OD. When the bushing is removed that neck would normally spring back(outward) ~1thou leaving ~1thou interference fit for the bullet. Seating bullet bearing in this neck will not up size it & neither will an expander(button/mandrel). The bullet is held with ~1thou hoop expansive force applied to seated bearing. That's probably enough to shoot today, but over a month or two this will change. The gripping force will drop over time as the counter to last sizing action(downsizing) continues.
Of course there is an opposite scenario;
Someone downsizes with a bushing to 4thou under loaded OD, and then expands the normal neck at cal. It springs back ~1thou(inward) providing as much tension. Over time this will increase 1/4-1/2thou's worth of tension(even while the hoop is held around the bullet). This can be good or bad for you.
There is no dimensional change with bullets seated, but the tension holding can change. You can pull a bullet and measure the hoop change. Actually, you can measure a FL sized case and watch this at any sized diameter, including shoulder bump, and even watch your primers creep over time.
I've found that it takes a plan to load ammo months in advance of a hunt to expect it to shoot the same as fresh ammo.
I'm just throwin this out there, because the implication that we should just continue to downsize necks more & more until a target proves something, is really a generalization for something real. It's something that could be measured, understood, and handled logically.
Peterbilt2007, are you sizing more or less LENGTH of the neck than seated bullet bearing?