Either that or flaring the case too much for loading. The case mouth should only be flared deep enough to allow the flat base of the bullet to move past the lip of the mouth to engage the inside of the case wall before being seated; I usually flare about 0.065-0.070" deep. I don't crimp my semiauto loads (but I only shoot them in semiauto pistols). I load 9mm, .40S&W, 10mm Auto and .45 Auto; never had any issues due to an out of spec case mouth diameter not allowing full seating in the chamber (headspacing), or feeding issues.

Did I read the OP's post correctly? He runs a completed round through a sizing die (minus the depriming pin)? I've never tried it, because I never figured it was intended, or would even work. I.D. of my RCBS .45 die is 0.464", and the O.D. of a completed .45 Auto round is 0.473" along the bullet seat area. For a completed round to fit inside the die, it would have to compress the bullet far enough to allow the case to size down to 0.464" (my empty cases come out of the sizing die at 0.466 due to a miniscule rebound of the brass). A competed round coming out of the sizing die (must take some real elbow grease) would be far less than the SAAMI spec of 0.473" diameter. I used digital calipers to obtain the above measurements, from my own dies and reloaded ammunition. My pistol runs perfectly (Springfield 1911A1) on my ammo.

Now, if the above posters are running .45 Auto revolvers with possibly different chamber dimensions, in the words of Roseanne Rosanna Danna, "never mind".