Most .45 Colt chambers are sloppy, so that at least partial sizing is necessary.
Modern .45 Colt carbide dies work the brass too much and case life is poor.
I do not full-length size, but partially size the front half of the case only, using a backed-off old RCBS steel die. I then use an RCBS cowboy expander with .453" diameter expander plug to slightly expand and flare the case mouth. Bullet can then be hand-started and then seated to length. Crimping is done separately using the Redding Profile Crimp die which gently profiles the case body. These rounds shoot well in two pre-WW2 Colts, an S&W 625, modern Ubertis, Piettas and Rugers as well as a Rossi carbine.
I don't size bullets smaller for the Rugers, one size fits all.