I fire .452, .453, and .454" lead bullets in my .45s. You have to know the groove-to-groove diameter of your barrel to know the minimum size lead bullet to use (groove diameter + 0.001). You can measure the I.D. of fired cases to determine the maximum size lead bullet to use (case ID at case mouth - 0.001). Then, you can try a couple different sizes and see how they work.
For most .45ACPs, you will want a .452 or .453 bullet.
Never assume that your pistol barrel is 0.451" groove-to-groove. Slug it and know.
When you reload, take out your barrel (or cylinder from your revolver) for use as a case gage.
Load a couple of dummy rounds (no primer or powder) to verify fit and feeding of your reloads.
Remember, the COL (OAL) listed in the manuals is just a suggestion. You will want to use the longest COL that fits in your magazine (or cylinder) and feeds and chambers in your gun. This allows minimum pressure and almost always much improved accuracy.
Ideal COL is about 0.002" off the lede/rifling, but your magazine and barrel will tell you what they want.
You can look when you drop a sized case in your barrel that almost all pistol cases are too short for proper headspacing and, except for rimmed, belted, or bottleneck cases, you will almost certainly never need to trim a case.
Some people load their lead bullets so they just kiss the lede/rifling and they establish near perfect headspace that way. This works great with midrange target/bullseye loads with lead bullets where you work up from the starting or even less than starting load. I have NEVER seen any pressure signs in my guns even working up to near max (standard ball load performance), but you have to start low and see what works in your pistol.
All anyone online can tell you is what works for them and how you need to work up to what they are doing.
Read the manuals, work up from starting loads, and if you want to vary a certain step (such as trying different COLs), only change that one variable and work up from the starting load.
Always keep records of you load (cases, bullets, actual weights, powder and lot number, charge weight, COL, primer used, possibly which dies you used, and change in standard loading procedure, date loaded, date fired, review of targets (group size, distance, # of shots, how the loads felt, and any other comments). You need to keep records so you know what you have done.
I prefer to use an Excel spreadsheet, but some like to have actual hard-bound books where they can place pictures or actual targets.