Can you use .45 Colt dies to load .45Auto?
 

Is there any reason I could not use my .45 Colt dies to load the .45 auto?
If so, are there any "tricks" to doing this? Like maybe having to expand the case a little more . . .

I have never tried it but that does not mean it wouldn't work. Off the top of my head I think seating could work but resizing would not for obvious reasons. You probably would not be able to taper crimp using the .45LC die either.

I went ahead and tride a few. Sizing seemed to be just fine. Primers came out and all. But when using the expander die, there seemed to be slight bulge in the case about halfway up. As if the case was being squeezed or smashed. Was not over expanding as I kept a close watch on when the bullet was just entering case as if to seat the bullet.

Before you make too many I would make sure they are fitting properly in the chamber.

While I might be brought to believe that 45colt dies could be used to assemble 45auto ammunition, I would never do so myself, nor would I want to be on the range next to anyone that saw fit to do so. I've heard of guys doing it, but I've also heard of guys surfing on top of cars down the highway for fun... I wouldn't partake in either personally.

My gut tells me that you're going to have issues, if not in the first load, then eventually. The colt dies are designed for a base diameter of 0.480", whereas your acp chamber should be spec'd for a base of 0.476 with a neck of 0.473". I'd imagine neck tension will be light, i.e. under tension when seating, since the 45colt die diameter will be too large - which might lead to the bullet being pushed deeper into the case during feeding, which may cause an unsafe overpressure condition. The larger diameter may not feed well, but you may avoid that issue if you have a sloppy factory chamber. The bullets being fairly loose in the neck would be my largest concern, and how that may effect feeding reliability and/or blow my piston apart by compressing the load under an action rammed bullet. You just won't get any crimp on your seater die, and MOST 45 colt dies are set up with roll crimp anyway, whereas you NEED a taper crimp in the 45auto.

My hands and eyes are more valuable to me than the pricetag of ANY die set. Don't be dumb, buy the right dies.

I don't trust the results so far.
Not gonna try it.

I ask why other than the obvious of MAYBE being able to do it. Dies are too cheap of cost in comparision to personal injury.