Live45 is right on target
Very likely you will not experience any problems at all, but you asked what to watch out for. 45 ACP is probably the easiest semi-auto pistol cartridge to load.
Bullseye is reputed to be ideal for 45 ACP, but Unique is my favorite. I don't usually give load recipes (nor take them) on forums. The powder manufacturers' web sites and my loading manuals are more reliable (that means safer) sources. Anyone can make a typographical error when postingg. (see?
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Live45 said:
Set it so that you just barely bell the case enough to set the bullet in the case mouth. I don't use a taper crimping die so this is a critical adjustment for me. Remove the barrel from your gun and make sure that a newly loaded round will "drop" into the chamber as far as a factory round and then fall out on it's own when the barrel is inverted. If your rounds do this you should be good to go.
The chamber check is sometimes known as the "plunk" test. If the cartridge drops by gravity alone into the chamber it should make a nice, hollow (because of the hollow barrel) plunk as the case mouth stops firmly against the step in the chamber.
Then, ideally, it should fall out of the chamber by gravity when you up-end the barrel.
Or, you can buy a chamber gauge if you don't want to bother with your barrel.
On expanding the case mouth. What has been said about not expanding too much is very important. The bullet is retained in the case by friction more than by crimp. This is vitally important to semi-auto arms in two directions.
You want good bullet tension (retention or grip) so that, upon ignition, pressure builds up inside the case before the bullet starts moving. This is important because smokeless powders need to be up into their optimal pressure range in order to achieve a consistent burn.
In the other direction, you want to be sure that the bullet is not forced deeper into the case as it cycles through the action and chambers.
Bullet setback can cause dramatic increases in chamber pressure.
You can test your loaded ammo by measuring its length before and after cycling a round through your action several times. If you get bullet setback, try another (one not having been set back) round and press the nose against your loading bench and see how much force it takes to press the bullet deeper in the case. Adjust your loading procedure accordingly. Primarily, this will be reducing the amount or depth of case mouth flare (even to the point of reducing the diameter of the expanding mandrel with emery cloth). Simply increasing the extent of the taper crimp is not usually helpful.
This advice applies to all ammunition that headspaces on the case mouth (and a lot of it applies to most other ammo, too).
Good luck. Thanks for asking our advice.
Lost Sheep