In my Hornady manual it says to use no crimpat all or a light crimp when loading 45 ACP. True or false. Opinions welcomed along with facts. Thanks in advance.

Use a taper crimp.

Taper crimping is best. Roll crimping lead bullets can cause accuracy degradation and poor ignition. I use a Lee Factory Crimp die.

In my youth I shot a lot of IPSC with a Colt GM .45 ACP. Always using ammo I had reloaded. 45 ACP headspaces on the case mouth. If you use a roll crimp you can adversely affect that relationship. Conversly, if you don't crimp at all you face the prospect of having the projectile rammed down the case during the feeding cycle, again not nice.

The answer is to use a taper crimp. Most manufacturers produce a taper crimp die. It allows you to have a firm reliable crimp and still have correct headspacing on the case mouth. Generally good practice to use the taper crimp as a separate stage after bullet seating.

The above only applies if you're using an auto.

My RCBS die set produces a nice taper crimp as it seats the bullet.

If you decide to crimp the 45 ACP, a light taper crimp is the way to go. When loading for target shooting you don’t need to crimp but there isn’t a downside to it if you do and there’s a lot of competitors who don’t crimp their cases, as proper case tension will hold the bullet securely in the magazine and you’ll get no set back while feeding cast or jacketed bullets.

Myself, I lightly taper crimp just for peace of mind that I have removed the entire bell on the case mouth – finished size at the mouth will run 0.4700” to 0.4705” with federal cases and either 0.451” or 0.452” bullets. I do my seating and crimping in 2 separate operations on a progressive reloader. Hunting/killing loads with heavy cast at 950/1,000fps I’ll taper crimp to 0.469" just for peace of mind, as there’s no real reason it needs that much crimp – even the 255 grain BB loads at 950/975fps are 0.4700” at the case mouth using starline +P brass. If it makes you feel better, do it, as it won’t hurt anything unless you go way overboard on the crimp like 0.465” or more – then accuracy will probably take a hike on ya.

I like to use a taper crimp as the 45 ACP headspaces on the case mouth.

I concur; taper crimp, with all types of bullets in the .45 ACP in the semi-auto platform.

I don't post often but just had too on this subject.
"In my Hornady manual it says to use no crimpat all or a light crimp when loading 45 ACP."
I have before me a new box of Hornady 200 gr XTP factory ammo.
I looked at the cartridges just to get a good look at a box of pretty ammo of which Hornady ammo is some of the nicest looking ammo one will see.
I looked at the way it was assembled and noticed that on all the cases the mouth was, even to the naked eye, taper crimped quite heavy.
I pulled a bullet and the case was taper crimped so hard that the bullet was indented to a pretty good amount.
I thought I have some Speer ammo and Winchester ammo in 45 ACP and will check it. Waa-laa the same thing. The cases were crimped so hard that the bullets were indented.
Why would Hornady say to use no crimp at all or a light crimp when loading 45 ACP.
Makes one wonder doesn't it
Kinda like most parents are with their children "don't do as I do do as I say" Kinda type deal.
I now taper crimp on the heavy side now. Not as heavy as the Hornady ammo but more than a light taper crimp.
Of course do as you please. But I have read the same thing and now I wonder about load books even more.
Made me pause to think a little.

I have been shooting USPSA for 12 years and shoot between 3500-4500 rounds a year. I load both cast and jacketed bullets. I have never crimped a round ever. And have never had a failure. Non of my friends who reload for USPSA crimp either. I have a buddy who a grand master shooter and he shoots 10,000 rounds + a year. Only because he has sponsors and he reloads and never crimps.
I imagine the factory crimps only because how the rounds are handled from the factories. They are banged bounced and dropped down tubes into boxes on a mass scale. Even with progressive reloading at home you tend not to torture your rounds like factories do. If you have a question about the factory ammo call Hornady, I bet they will tell why they do it but say you don't have to.

I always just turned the case into straight too and believe that is good enough but now I do taper crimp slightly heavier than I did.
If Hornady, Speer and Winchester taper crimp fairly heavy they must have good reasons too.
It could be the harsh handling etc..
But how harsh would it have to be to cause a problem with properly loaded and lightly taper crimped rounds for the light taper crimp to cause a problem?
I may, on my next days ,subject a round of 45 ACP ammo that has been just very lightly crimped to some harsh handling (with no powder and primer) and see just what one will take without moving the bullet.

I have actually been wondering if they want a slight crimp just to counter act the flair from the expanding die. Just a thought...

I have the same question on 10mm reloads. I have a Lee factory crimp die that sizes the case on the up stroke and the down stroke during the crimp process. You can adjust the amount of crimp from none to heavy. I would think that would remove the flair from the expanding die. However I have never reloaded for
a semi-auto. Just rifle and 460xvr. Any thoughts.